DS1923_11_技术文档

19-4991; Rev 4; 4/11

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

DS1923

♦ Quick Access to Alarmed Devices Through 1-Wire

General Description

Conditional Search Function

®

The DS1923 temperature/humidity logger iButton is a

♦ 512 Bytes of General-Purpose Memory Plus 64

rugged, self-sufficient system that measures temperature

and/or humidity and records the result in a protected

memory section. The recording is done at a user-defined

rate. A total of 8192 8-bit readings or 4096 16-bit readings,

taken at equidistant intervals ranging from 1s to 273hr, can

be stored. Additionally, 512 bytes of SRAM store applica-

tion-specific information and 64 bytes store calibration

data. A mission to collect data can be programmed to

begin immediately, after a user-defined delay, or after a

temperature alarm. Access to the memory and control

functions can be password protected. The DS1923 is con-

figured and communicates with a host-computing device

Bytes of Calibration Memory

♦ Two-Level Password Protection of All Memory

and Configuration Registers

♦ Communicates to Host with a Single Digital Signal

at Up to 15.4kbps at Standard Speed or Up to

125kbps in Overdrive Mode Using 1-Wire Protocol

♦ Individually Calibrated in an NIST-Traceable Chamber

♦ Calibration Coefficients for Temperature and

Humidity Factory Programmed Into Nonvolatile

(NV) Memory

®

through the serial 1-Wire protocol, which requires only a

Common iButton Features

single data lead and a ground return. Every DS1923 is

factory lasered with a guaranteed unique 64-bit registra-

tion number that allows for absolute traceability. The

durable stainless-steel package is highly resistant to envi-

ronmental hazards such as dirt, moisture, and shock.

Accessories permit the DS1923 to be mounted on almost

any object, including containers, pallets, and bags.

♦ Digital Identification and Information by

Momentary Contact

♦ Unique Factory-Lasered 64-Bit Registration Number

Ensures Error-Free Device Selection and Absolute

Traceability Because No Two Parts Are Alike

♦ Built-In Multidrop Controller for 1-Wire Net

♦ Chip-Based Data Carrier Compactly Stores Information

♦ Data Can Be Accessed While Affixed to Object

♦ Button Shape is Self-Aligning with Cup-Shaped Probes

Applications

Temperature and Humidity Logging in Food

Preparation and Processing

♦ Durable Stainless-Steel Case Engraved with

Transportation of Temperature-Sensitive and

Humidity-Sensitive Goods, Industrial Production

Registration Number Withstands Harsh Environments

♦ Easily Affixed with Self-Stick Adhesive Backing,

Latched by Its Flange, or Locked with a Ring

Pressed Onto Its Rim

Warehouse Monitoring

Environmental Studies/Monitoring

Features

♦ Presence Detector Acknowledges When Reader

♦ Digital Hygrometer Measures Humidity with 8-Bit

First Applies Voltage

(0.6%RH) or 12-Bit (0.04%RH) Resolution

♦ Meets UL 913, 5th Ed., Rev. 1997-02-24; Intrinsically

Safe Apparatus: Approved Under Entity Concept

for Use in Class I, Division 1, Group A, B, C, and D

Locations

♦ Operating Range: -20°C to +85°C; 0 to 100%RH

(see Safe Operating Range Graph)

♦ Automatically Wakes Up, Measures Temperature

and/or Humidity, and Stores Values in 8KB of

Data-Log Memory in 8-Bit or 16-Bit Format

Ordering Information

PART

TEMP RANGE

PIN-PACKAGE

♦ Digital Thermometer Measures Temperature with

DS1923-F5#

-20°C to +85°C

F5 iButton

8-Bit (0.5°C) or 11-Bit (0.0625°C) Resolution

#Denotes a RoHS-compliant device that may include lead(Pb)

that is exempt under the RoHS requirements.

♦ Temperature Accuracy Better Than 0.5°C from

-10°C to +65°C with Software Correction

Examples of Accessories

♦ Built-In Capacitive Polymer Humidity Sensor for

Humidity Logging

PART

ACCESSORY

Self-Stick Adhesive Pad

Multipurpose Clip

Mounting Lock Ring

Snap-In FOB

♦ Hydrophobic Filter Protects Sensor Against Dust, Dirt,

DS9096P

DS9101

Contaminants, and Water Droplets/Condensation

♦ Sampling Rate from 1s Up to 273hr

DS9093RA

DS9093A

DS9092

♦ Programmable Recording Start Delay After Elapsed

Time or Upon a Temperature Alarm Trip Point

iButton Probe

♦ Programmable High and Low Trip Points for

Pin Configuration appears at end of data sheet.

Temperature and Humidity Alarms

iButton and 1-Wire are registered trademarks of Maxim Integrated Products, Inc.

________________________________________________________________ Maxim Integrated Products

1

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,

or visit Maxim’s website at www.maxim-ic.com.

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

ABSOLUTE MAXIMUM RATINGS

IO Voltage Range Relative to GND ..........................-0.3V to +6V

IO Sink Current....................................................................20mA

Operating Temperature

and Humidity Range ................-20°C to +85°C, 0 to 100%RH*

Storage Temperature

and Humidity Range ................-40°C to +85°C, 0 to 100%RH*

*See the Safe Operating Range graph.

DS1923

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional

operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to

absolute maximum rating conditions for extended periods may affect device reliability.

ELECTRICAL CHARACTERISTICS

(V

PUP

= +3.0V to +5.25V, T = -20°C to +85°C.) (Note 31)

A

PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

IO PIN: GENERAL DATA

1-Wire Pullup Resistance

Input Capacitance

R

(Notes 1, 2)

(Note 3)

2.2

800

10

kꢀ

pF

μA

V

PUP

C

100

6

IO

Input Load Current

I

L

IO pin at V

PUP

High-to-Low Switching Threshold

Input Low Voltage

V

(Notes 4, 5)

(Notes 1, 6)

(Notes 4, 7)

(Note 8)

0.4

3.2

0.3

3.4

N/A

0.4

TL

V

IL

Low-to-High Switching Threshold

Switching Hysteresis

V

0.7

V

TH

HY

OL

V

0.09

V

Output Low Voltage

At 4mA (Note 9)

V

Standard speed, R

= 2.2kꢀ

5

2

PUP

Overdrive speed, R

= 2.2kꢀ

PUP

Recovery Time

(Note 1)

t

μs

REC

REH

Overdrive speed directly prior to reset

pulse, R = 2.2kꢀ

5

PUP

Rising-Edge Hold-Off Time

Time-Slot Duration (Note 1)

(Note 10)

0.6

65

8

2.0

μs

Standard speed

t

Overdrive speed, V

> 4.5V

SLOT

PUP

Overdrive speed (Note 11)

IO PIN: 1-Wire RESET, PRESENCE-DETECT CYCLE

Standard speed, V

9.5

> 4.5V

480

690

48

720

80

60

63.5

7

PUP

Standard speed (Note 11)

Overdrive speed, V > 4.5V

Reset Low Time (Note 1)

t

μs

RSTL

PUP

Overdrive speed (Note 11)

Standard speed, V > 4.5V

70

15

PUP

Presence-Detect High Time

t

μs

Standard speed (Note 11)

Overdrive speed (Note 11)

15

PDH

2

Standard speed, V

Standard speed

Overdrive speed

> 4.5V

1.5

0.15

5

PUP

Presence-Detect Fall Time

(Note 12)

t

8

FPD

1

2

_______________________________________________________________________________________

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

DS1923

ELECTRICAL CHARACTERISTICS (continued)

(V

PUP

= +3.0V to +5.25V, T = -20°C to +85°C.) (Note 31)

A

PARAMETER

SYMBOL

CONDITIONS

Standard speed, V > 4.5V

MIN

60

7

TYP

MAX

240

287

24

UNITS

PUP

Standard speed (Note 11)

Overdrive speed, V > 4.5V (Note 11)

Presence-Detect Low Time

t

μs

PDL

PUP

Overdrive speed (Note 11)

7

28

Standard speed, V

Standard speed

Overdrive speed

> 4.5V

65

71.5

8

75

PUP

Presence-Detect Sample Time

(Note 1)

t

μs

75

MSP

9

IO PIN: 1-Wire WRITE

Standard speed

60

6

120

12

Write-Zero Low Time

(Notes 1, 13)

t

μs

Overdrive speed, V

> 4.5V (Note 11)

W0L

PUP

Overdrive speed (Note 11)

Standard speed

7.5

5

12

15

Write-One Low Time

(Notes 1, 13)

t

W1L

Overdrive speed

1

1.95

IO PIN: 1-Wire READ

Standard speed

Overdrive speed

Standard speed

Overdrive speed

5

1

15 - ꢁ

1.95 - ꢁ

15

Read Low Time

(Notes 1, 14)

t

μs

RL

t

+ ꢁ

Read Sample Time

(Notes 1, 14)

RL

t

MSR

+ ꢁ

1.95

REAL-TIME CLOCK (RTC)

Min/

Month

Accuracy

See RTC Accuracy graph

Frequency Deviation

ꢂ

F

-20°C to +85°C

-300

+60

ppm

TEMPERATURE CONVERTER

8-bit mode (Note 15)

16-bit mode (11 bits)

30

75

Conversion Time

t

ms

s

CONV

240

600

Thermal Response Time

Constant

ꢃ

iButton package (Note 16)

(Notes 15, 17, 18, 19)

130

RESP

ꢂꢄ

Conversion Error Without

Software Correction

See the Temperature

Accuracy graph

°C

Conversion Error with Software

Correction

See the Temperature

Accuracy graph

ꢂꢄ

HUMIDITY CONVERTER (Note 20)

Humidity Response Time

Constant

ꢃ

Slow moving air (Note 21)

30

s

RH

8

0.64

0

12

Bits

%RH

RH Resolution

RH Range

(Note 22)

(Note 23)

0.04

100

_______________________________________________________________________________________

3

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

ELECTRICAL CHARACTERISTICS (continued)

(V

PUP

= +3.0V to +5.25V, T = -20°C to +85°C.) (Note 31)

A

PARAMETER

SYMBOL

CONDITIONS

With software correction

(Notes 18, 19, 24, 25, 26)

With software correction (Note 18)

(Notes 27, 28)

MIN

TYP

MAX

UNITS

RH Accuracy and

Interchangeability

5

%RH

RH Nonlinearity

RH Hysteresis

RH Repeatability

< 1

0.5

DS1923

%RH

(Note 29)

%RH/

year

Long-Term Stability

At 50%RH (Note 30)

< 1.0

Note 1: System requirement.

Note 2: Maximum allowable pullup resistance is a function of the number of 1-Wire devices in the system and 1-Wire recovery

times. The specified value here applies to systems with only one device and with the minimum 1-Wire recovery times. For

more heavily loaded systems, an active pullup such as that in the DS2480B may be required.

Note 3: Capacitance on the data pin could be 800pF when V

is first applied. If a 2.2kΩ resistor is used to pull up the data line,

PUP

2.5μs after V

has been applied, the parasite capacitance does not affect normal communications.

PUP

Note 4:

V

and V are functions of the internal supply voltage, which is a function of V

and the 1-Wire recovery times. The

TL

TH

PUP

and V maximum specifications are valid at V

= 5.25V. In any case, V < V < V

.

TL

PUP

TL

TH

PUP

Note 5: Voltage below which, during a falling edge on IO, a logic 0 is detected.

Note 6: The voltage on IO must be less than or equal to V whenever the master drives the line low.

ILMAX

Note 7: Voltage above which, during a rising edge on IO, a logic 1 is detected.

Note 8: After V is crossed during a rising edge on IO, the voltage on IO must drop by V to be detected as logic 0.

TH

HY

Note 9: The I-V characteristic is linear for voltages less than 1V.

Note 10: The earliest recognition of a negative edge is possible at t

after V has been previously reached.

TH

REH

Note 11: Numbers in bold are not in compliance with the published iButton standards. See the Comparison Table.

Note 12: Interval during the negative edge on IO at the beginning of a presence-detect pulse between the time at which the voltage

is 90% of V

and the time at which the voltage is 10% of V

.

PUP

Note 13: ε in Figure 13 represents the time required for the pullup circuitry to pull the voltage on IO up from V to V . The actual

IL

TH

maximum duration for the master to pull the line low is t

+ t - ε and t

+ t - ε, respectively.

W0LMAX F

W1LMAX

F

Note 14: δ in Figure 13 represents the time required for the pullup circuitry to pull the voltage on IO up from V to the input high

IL

threshold of the bus master. The actual maximum duration for the master to pull the line low is t

Note 15: To conserve battery power, use 8-bit temperature logging whenever possible.

Note 16: This number was derived from a test conducted by Cemagref in Antony, France, in July 2000:

www.cemagref.fr/English/index.htm Test Report No. E42.

+ t .

RLMAX

F

Note 17: For software-corrected accuracy, assume correction using calibration coefficients with calibration equations for error

compensation.

Note 18: Software correction for humidity and temperature is handled automatically using the 1-Wire Viewer Software package

available at: www.ibutton.com.

Note 19: Warning: Not for use as the sole method of measuring or tracking temperature and/or humidity in products and articles

that could affect the health or safety of persons, plants, animals, or other living organisms, including but not limited to

foods, beverages, pharmaceuticals, medications, blood and blood products, organs, and flammable and combustible

products. User shall assure that redundant (or other primary) methods of testing and determining the handling methods,

quality, and fitness of the articles and products should be implemented. Temperature and/or humidity tracking with this

product, where the health or safety of the aforementioned persons or things could be adversely affected, is only recom-

mended when supplemental or redundant information sources are used. Data-logger products are 100% tested and cali-

brated at time of manufacture by Maxim to ensure that they meet all data sheet parameters, including temperature

accuracy. User shall be responsible for proper use and storage of this product. As with any sensor-based product, user

shall also be responsible for occasionally rechecking the accuracy of the product to ensure it is still operating properly.

Note 20: All humidity specifications are determined at +25°C except where specifically indicated.

Note 21: Response time is determined by measuring the 1/e point as the device transitions from 40%RH to 90%RH or 90%RH to

40%RH, whichever is slower. Test was performed at 5L/min airflow.

Note 22: All DS1923 humidity measurements are 12-bit readings. Missioning determines 8-bit or 16-bit data logging. Battery life-

time is the same no matter what RH resolution is logged.

4

_______________________________________________________________________________________

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

DS1923

ELECTRICAL CHARACTERISTICS (continued)

(V

PUP

= +3.0V to +5.25V, T = -20°C to +85°C.) (Note 31)

A

Note 23: Reliability studies have shown that the device survives a minimum of 1000 cycles of condensation and drying, but this

product is not guaranteed for extended use in condensing environments.

Note 24: Software-corrected accuracy is accomplished using the method detailed in the Software Correction Algorithm for

Temperature section.

Note 25: Every DS1923 device is measured and calibrated in a controlled, NIST-traceable RH environment.

Note 26: Higher accuracy versions may be available. Contact the factory for details.

Note 27: If this device is exposed to a high humidity environment (> 70%RH), and then exposed to a lower RH environment, the

device reads high for a period of time. The device typically reads within +0.5%RH at 20%RH, 30 minutes after being

exposed to continuous 80%RH for 30 minutes.

Note 28: All capacitive RH sensors can change their reading depending upon how long they have spent at high (> 70%RH) or low

RH (< 20%RH). This effect is called saturation drift and can be compensated through software, as described in the

Software Saturation Drift Compensation section.

Note 29: Individual RH readings always include a noise component (repeatability). To minimize measurement error, average as

many samples as is reasonable.

Note 30: Like all relative humidity sensors, when exposed to contaminants and/or conditions toward the limits of the safe operating

range, accuracy degradation can result (see the Safe Operating Range graph). For maximum long-term stability, the sen-

sor should not be exposed or subjected to organic solvents, corrosive agents (e.g., strong acids, SO , H SO , CI , HCL,

2

4

2

H S) and strong bases (i.e., compounds with a pH greater than 7). Dust settling on the filter surface does not affect the

2

sensor performance except to possibly decrease the speed of response. For more information on the RH sensor’s toler-

ance to chemicals visit: http://content.honeywell.com/sensing/prodinfo/humiditymoisture/technical/c15_144.pdf.

Note 31: Guaranteed by design; not production tested to -20°C.

COMPARISON TABLE

LEGACY VALUES

DS1923 VALUES

STANDARD SPEED

(μs)

OVERDRIVE SPEED

(μs)

STANDARD SPEED

(μs)

OVERDRIVE SPEED

(μs)

PARAMETER

MIN

61

MAX

MIN

7

MAX

MIN

65^*

690

15

MAX

MIN

9.5

70

2

MAX

t

(including t

)

(undefined)

60

(undefined)

720

(undefined)

SLOT

REC

480

15

48

2

80

6

80

7

RSTL

PDH

PDL

63.5

60

240

8

24

16

60

287

7

28

12

60

120

6

60

120

7.5

W0L

*Intentional change; longer recovery time requirement due to modified 1-Wire front-end.

Note: Numbers in bold are not in compliance with the published iButton standards.

iButton CAN PHYSICAL SPECIFICATION

SIZE

See the Package Information section.

WEIGHT

Ca. 5.0 grams

Meets UL 913, 5th Ed., Rev. 1997-02-24; Intrinsically Safe Apparatus, approval under Entity Concept for use in

Class I, Division 1, Group A, B, C, and D Locations.

SAFETY

_______________________________________________________________________________________

5

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

Safe Operating Range

100

80

60

40

20

0

DS1923

SAFE OPERATING ZONE

STORAGE

ONLY

-40

-20

0

20

40

60

80

TEMPERATURE (°C)

Temperature Accuracy

2.0

1.5

1.0

0.5

0

UNCORRECTED MAXIMUM ERROR

SW CORRECTED MAXIMUM ERROR

SW CORRECTED MINIMUM ERROR

UNCORRECTED MINIMUM ERROR

-0.5

-1.0

-20

-10

0

10

20

30

40

50

60

70

80

TEMPERATURE (°C)

NOTE: THE GRAPHS ARE BASED ON 11-BIT DATA.

6

_______________________________________________________________________________________

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

DS1923

Minimum Lifetime vs. Temperature, Slow Sampling (Temperature Only)

EVERY MINUTE

EVERY 3 MINUTES

NO SAMPLES

EVERY 10 MINUTES

OSCILLATOR OFF

EVERY 60 MINUTES

10

9

8

7

6

5

4

3

2

1

0

-20

-10

0

10

20

30

40

50

60

70

80

TEMPERATURE (°C)

EVERY MINUTE

EVERY 3 MINUTES

EVERY 10 MINUTES

NO SAMPLES

EVERY 30 MINUTES

OSCILLATOR OFF

EVERY 60 MINUTES

EVERY 300 MINUTES

10

9

8

7

6

5

4

3

2

1

0

-20

-10

0

10

20

30

40

50

60

70

80

TEMPERATURE (°C)

_______________________________________________________________________________________

7

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

Minimum Lifetime vs. Temperature, Fast Sampling (Temperature Only)

EVERY SECOND

EVERY 3 SECONDS

EVERY 60 SECONDS

EVERY 10 SECONDS

EVERY 30 SECONDS

350

300

250

200

150

100

50

DS1923

0

-20

-10

0

10

20

30

40

50

60

70

80

TEMPERATURE (°C)

EVERY SECOND

EVERY 3 SECONDS

EVERY 60 SECONDS

EVERY 10 SECONDS

EVERY 30 SECONDS

100

80

60

40

20

0

-20

-10

0

10

20

30

40

50

60

70

80

TEMPERATURE (°C)

8

_______________________________________________________________________________________

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

DS1923

Minimum Lifetime vs. Temperature, Slow Sampling

(Temperature with Humidity)

EVERY MINUTE

EVERY 3 MINUTES

NO SAMPLES

EVERY 10 MINUTES

OSCILLATOR OFF

EVERY 60 MINUTES

10

9

8

7

6

5

4

3

2

1

0

-20

-10

0

10

20

30

40

50

60

70

80

TEMPERATURE (°C)

Minimum Lifetime vs. Temperature, Fast Sampling

(Temperature with Humidity)

EVERY SECOND

EVERY 3 SECONDS

EVERY 60 SECONDS

EVERY 10 SECONDS

EVERY 30 SECONDS

350

300

250

200

150

100

50

0

-20

-10

0

10

20

30

40

50

60

70

80

TEMPERATURE (°C)

_______________________________________________________________________________________

9

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

Minimum Product Lifetime vs. Sample Rate (Temperature Only)

10

0°C

+40°C

+60°C

DS1923

+75°C

1

+85°C

0.1

0.01

0.1

1

10

100

MINUTES BETWEEN SAMPLES

NOTE: WITH HUMIDITY LOGGING ACTIVATED, THE LIFETIME IS REDUCED BY LESS THAN 11% FOR THE SAMPLE RATES OF 3MIN. AND SLOWER, AND BY A

MAXIMUM OF 20% FOR SAMPLE RATES OF 1MIN. AND FASTER.

10

0°C

+40°C

+60°C

+75°C

1

+85°C

0.1

0.01

0.001

0.01

0.1

1

10

100

MINUTES BETWEEN SAMPLES

NOTE: WITH HUMIDITY LOGGING ACTIVATED, THE LIFETIME IS REDUCED BY A MAXIMUM OF 4%. THE INCREMENTAL ENERGY CONSUMED BY HUMIDITY

LOGGING IS INDEPENDENT OF THE HUMIDITY LOGGING RESOLUTION.

10 ______________________________________________________________________________________

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

DS1923

RTC Accuracy (Typical)

2.0

1.0

0.0

-1.0

-2.0

-3.0

-4.0

-5.0

-20

-10

0

10

20

30

40

50

60

70

80

TEMPERATURE (°C)

This software also includes drivers for the serial and USB

port of a PC and routines to access the general-purpose

memory for storing application-specific or equipment-

specific data files.

Detailed Description

The DS1923 is an ideal device to monitor for extended

periods of time the temperature and humidity of any

object it is attached to or shipped with, such as fresh

produce, medical drugs and supplies, and for use in

refrigerators and freezers, as well as for logging climat-

ic data during the transport of sensitive objects and

critical processes such as curing. A 1.27mm diameter

hole in the lid of the device allows for air to reach the

humidity sensor. The rest of the electronics inside the

DS1923 is sealed so that it is not exposed to ambient

humidity. Note that the initial sealing level of the

DS1923 achieves the equivalent of IP56. Aging and use

conditions can degrade the integrity of the seal over

time, so for applications with significant exposure to liq-

uids, sprays, or other similar environments, it is recom-

mended to place the Hygrochron™ under a shield to

protect it (refer to Application Note 4126: Understanding

the IP (Ingress Protection) Ratings of iButton Data

Loggers and Capsule). The hydrophobic filter may not

protect the DS1923 from destruction in the event of full

submersion in liquid. Software for setup and data

retrieval through the 1-Wire interface is available for free

download from the iButton website (www.ibutton.com).

All iButton data loggers are calibrated/validated against

NIST traceable reference devices. Maxim offers a web

application to generate validation certificates for the

DS1922L, DS1922T, DS1922E, and DS1923 (tempera-

ture portion only) data loggers. Input is the iButton’s

ROM code (or list of codes) and the output is a valida-

tion certificate in PDF format. For more information,

®

refer to Application Note 4629: iButton Data-Logger

Calibration and NIST Certificate FAQs.

Overview

The block diagram in Figure 1 shows the relationships

between the major control and memory sections of the

DS1923. The device has six main data components:

64-bit lasered ROM; 256-bit scratchpad; 512-byte gen-

eral-purpose SRAM; two 256-bit register pages of time-

keeping, control, status, and counter registers and

passwords; 64 bytes of calibration memory; and 8192

bytes of data-logging memory. Except for the ROM

and the scratchpad, all other memory is arranged in a

single linear address space. The data-logging memo-

ry, counter registers, and several other registers are

Hygrochron is a trademark of Maxim Integrated Products, Inc.

______________________________________________________________________________________ 11

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

ROM

FUNCTION

CONTROL

64-BIT

LASERED

ROM

PARASITE-POWERED

CIRCUITRY

1-Wire PORT IO

DS1923

256-BIT

SCRATCHPAD

MEMORY

FUNCTION

CONTROL

3V LITHIUM

DS1923

GENERAL-PURPOSE

SRAM

(512 BYTES)

INTERNAL

32.768kHz

TIMEKEEPING,

CONTROL REGISTERS,

AND COUNTERS

REGISTER PAGES

(64 BYTES)

OSCILLATOR

CALIBRATION MEMORY

(64 BYTES)

THERMAL

SENSE

ADC1

HUMIDITY

SENSOR AND

ADC2

CONTROL

LOGIC

DATA-LOG MEMORY

8KB

Figure 1. Block Diagram

read only for the user. Both register pages are write

protected while the device is programmed for a mis-

sion. The password registers, one for a read password

and another one for a read/write password, can only

be written, never read.

accessible and the master can provide any one of the

eight available commands. The protocol for these

memory and control function commands is described

in Figure 9. All data is read and written least signifi-

cant bit first.

Figure 2 shows the hierarchical structure of the 1-Wire

protocol. The bus master must first provide one of the

eight ROM function commands: Read ROM, Match

ROM, Search ROM, Conditional Search ROM, Skip

ROM, Overdrive-Skip ROM, Overdrive-Match ROM, or

Resume. Upon completion of an Overdrive-ROM com-

mand executed at standard speed, the device enters

overdrive mode, where all subsequent communication

occurs at a higher speed. The protocol required for

these ROM function commands is described in Figure

11. After a ROM function command is successfully exe-

cuted, the memory and control functions become

Parasite Power

The block diagram (Figure 1) shows the parasite-pow-

ered circuitry. This circuitry “steals” power whenever

the IO input is high. IO provides sufficient power as

long as the specified timing and voltage requirements

are met. The advantages of parasite power are two-

fold: 1) By parasiting off this input, battery power is not

consumed for 1-Wire ROM function commands, and

2) if the battery is exhausted for any reason, the ROM

may still be read normally. The remaining circuitry of

the DS1923 is solely operated by battery energy.

12 ______________________________________________________________________________________

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

DS1923

Understanding and Using Cyclic Redundancy Checks

with Maxim iButton Products.

64-Bit Lasered ROM

Each DS1923 contains a unique ROM code that is 64

bits long. The first 8 bits are a 1-Wire family code. The

next 48 bits are a unique serial number. The last 8 bits

are a cyclic redundancy check (CRC) of the first 56 bits

(see Figure 3 for details). The 1-Wire CRC is generated

using a polynomial generator consisting of a shift regis-

ter and XOR gates as shown in Figure 4. The polynomi-

The shift register bits are initialized to 0. Then, starting

with the least significant bit of the family code, one bit

at a time is shifted in. After the 8th bit of the family code

has been entered, the serial number is entered. After

the last bit of the serial number has been entered, the

shift register contains the CRC value. Shifting in the 8

bits of CRC returns the shift register to all 0s.

8

5

4

al is X + X + X + 1. Additional information about the

1-Wire CRC is available in Application Note 27:

1-Wire NET

BUS

MASTER

OTHER DEVICES

DS1923

COMMAND LEVEL:

AVAILABLE COMMANDS:

DATA FIELD AFFECTED:

READ ROM

64-BIT ROM, RC-FLAG

MATCH ROM

64-BIT ROM, RC-FLAG

SEARCH ROM

64-BIT ROM, RC-FLAG

1-Wire ROM

FUNCTION COMMANDS

CONDITIONAL SEARCH ROM

SKIP ROM

64-BIT ROM, RC-FLAG, ALARM FLAGS, SEARCH CONDITIONS

RC-FLAG

RESUME

RC-FLAG

OVERDRIVE-SKIP ROM

OVERDRIVE-MATCH ROM

RC-FLAG, OD-FLAG

64-BIT ROM, RC-FLAG, OD-FLAG

WRITE SCRATCHPAD

256-BIT SCRATCHPAD, FLAGS

READ SCRATCHPAD

256-BIT SCRATCHPAD

COPY SCRATCHPAD WITH PW

READ MEMORY WITH PW AND CRC

CLEAR MEMORY WITH PW

512-BYTE DATA MEMORY, REGISTERS, FLAGS, PASSWORDS

MEMORY, REGISTERS, PASSWORDS

MISSION TIMESTAMP, MISSION SAMPLES COUNTER,

START DELAY, ALARM FLAGS, PASSWORDS

MEMORY ADDRESSES 020Ch TO 020Fh

FLAGS, TIMESTAMP, MEMORY ADDRESSES

020Ch TO 020Fh (WHEN LOGGING)

FLAGS

DS1923-SPECIFIC

MEMORY/CONTROL FUNCTION

COMMANDS

FORCED CONVERSION

START MISSION WITH PW

STOP MISSION WITH PW

Figure 2. Hierarchical Structure for 1-Wire Protocol

MSB

LSB

8-BIT

CRC CODE

8-BIT FAMILY CODE

(41h)

48-BIT SERIAL NUMBER

MSB

LSB MSB

Figure 3. 64-Bit Lasered ROM

______________________________________________________________________________________ 13

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

8

5

4

POLYNOMIAL = X + X + X + 1

1ST

2ND

3RD

4TH

5TH

6TH

7TH

8TH

STAGE

DS1923

0

1

2

3

4

5

6

7

8

X

INPUT DATA

Figure 4. 1-Wire CRC Generator

32-BYTE INTERMEDIATE STORAGE

SCRATCHPAD

ADDRESS

32-BYTE GENERAL-PURPOSE SRAM

(R/W)

0000h TO 001Fh

0020h TO 01FFh

0200h TO 021Fh

0220h TO 023Fh

0240h TO 025Fh

0260h TO 027Fh

0280h TO 0FFFh

1000h TO 2FFFh

PAGE 0

GENERAL-PURPOSE SRAM (R/W)

32-BYTE REGISTER PAGE 1

32-BYTE REGISTER PAGE 2

PAGES 1 TO 15

PAGE 16

PAGE 17

CALIBRATION MEMORY PAGE 1 (R/W)

CALIBRATION MEMORY PAGE 2 (R/W)

(RESERVED FOR FUTURE EXTENSIONS)

DATA-LOG MEMORY (READ ONLY)

PAGE 18

PAGE 19

PAGES 20 TO 127

PAGES 128 TO 383

Figure 5. Memory Map

writing to the SRAM memory or the register pages.

The calibration memory holds data from the device

calibration that can be used to further improve the

accuracy of temperature and humidity readings. See

the Software Correction Algorithm sections for details.

The last byte of the calibration memory page stores an

8-bit CRC of the preceding 31 bytes. Page 19 is an

exact copy of the data in page 18. While the user can

overwrite the calibration memory, this is not recom-

mended. See the Security by Password section for

ways to protect the memory. The access type for the

Memory

Figure 5 shows the DS1923 memory map. Pages 0 to

15 contain 512 bytes of general-purpose SRAM. The

various registers to set up and control the device fill

pages 16 and 17, called register pages 1 and 2 (see

Figure 6 for details). Pages 18 and 19 can be used as

storage space for calibration data. The data-log log-

ging memory starts at address 1000h (page 128) and

extends over 256 pages. The memory pages 20 to

127 are reserved for future extensions. The scratch-

pad is an additional page that acts as a buffer when

14 ______________________________________________________________________________________

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

DS1923

register pages is register-specific and depends on

behavior of the write access logic (write scratchpad,

copy scratchpad), it is recommended to only write full

pages at a time. This also applies to the register

pages. See the Address Registers and Transfer

Status section for details.

whether the device is programmed for a mission.

Figure 6 shows the details. The data-log memory is

read only for the user. It is written solely under super-

vision of the on-chip control logic. Due to the special

ADDRESS

0200h

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

FUNCTION

ACCESS*

0

10 Seconds

10 Minutes

Single Seconds

Single Minutes

0201h

20 Hour

AM/PM

Real-

Time Clock

Registers

0202h

0203h

0204h

0

12/24

10 Hour

Single Hours

Single Date

R/W

R

0

10 Date

10

Months

CENT

0

Single Months

Single Years

0205h

0206h

0207h

0208h

0209h

020Ah

020Bh

020Ch

020Dh

020Eh

020Fh

10 Years

Low Byte

Sample

Rate

R/W

R

0

High Byte

Low Threshold

High Threshold

Low Threshold

High Threshold

Temperature

Alarms

Humidity

Alarms

Low Byte

0

Latest

Temperature

High Byte

Low Byte

High Byte

Latest

Humidity

R

Temperature

Alarm

0210h

0211h

0

1

0

1

0

1

0

1

0

1

ETHA

EHHA

ETLA

EHLA

R/W

R

Enable

Humidity

Alarm

1

Enable

0212h

0213h

0214h

0215h

0

1

0

1

0

SUTA

1

0

RO

1

0

TLFS

HLF

0

EHSS

EHL

THF

MIP

EOSC

ETL

TLF

0

RTC Control R/W

R

Mission

R/W

HLFS

HHF

Control

BOR

1

Alarm Status

R

General

Status

0

WFTA MEMCLR

0216h

0217h

0218h

Low Byte

Center Byte

High Byte

Start

Delay

Counter

R/W

R

*The left entry in the ACCESS column is valid between missions. The right entry shows the applicable access type while a

mission is in progress.

Figure 6. Register Pages Map

______________________________________________________________________________________ 15

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

ADDRESS

0219h

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

FUNCTION

ACCESS*

0

10 Seconds

10 Minutes

Single Seconds

Single Minutes

021Ah

20 Hour

AM/PM

021Bh

021Ch

021Dh

0

12/24

10 Hour

Single Hours

Single Date

Mission

Timestamp

R

9

0

10 Date

10

Months

CENT

0

Single Months

Single Years

021Eh

021Fh

0220h

0221h

0222h

0223h

0224h

0225h

0226h

0227h

0228h

…

10 Years

(No Function; Reads 00h)

Low Byte

—

R

Mission

Samples

Counter

Center Byte

High Byte

Low Byte

Device

Samples

Counter

R

Center Byte

High Byte

Configuration Code

EPW

Flavor

R

PW Control

R/W

First Byte

…

Read

Access

Password

W

R

—

R

022Fh

0230h

…

Eighth Byte

First Byte

…

Full

Access

Password

0237h

0238h

…

Eighth Byte

(No function; all these bytes read 00h)

—

023Fh

*The left entry in the ACCESS column is valid between missions. The right entry shows the applicable access type while a

mission is in progress.

Figure 6. Register Pages Map (continued)

16 ______________________________________________________________________________________

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

DS1923

Sample Rate

Detailed Register Descriptions

The content of the Sample Rate register (addresses

Timekeeping and Calendar

0206h, 0207h) specifies the time elapse (in seconds if

The RTC and calendar information is accessed by

EHSS = 1, or minutes if EHSS = 0) between two tem-

reading/writing the appropriate bytes in the register

perature/humidity-logging events. The sample rate can

page, address 0200h to 0205h. For readings to be

be any value from 1 to 16,383, coded as an unsigned

valid, all RTC registers must be read sequentially start-

14-bit binary number. If EHSS = 1, the shortest time

ing at address 0200h. Some of the RTC bits are set to

between logging events is 1s and the longest (sample

0. These bits always read 0 regardless of how they are

rate = 3FFFh) is 4.55hr. If EHSS = 0, the shortest is

written. The number representation of the RTC registers

1min and the longest time is 273.05hr (sample rate =

is binary-coded decimal (BCD) format.

3FFFh). The EHSS bit is located in the RTC Control reg-

The DS1923’s RTC can run in either 12hr or 24hr mode.

Bit 6 of the Hours register (address 0202h) is defined

as the 12hr or 24hr mode select bit. When high, the

12hr mode is selected. In the 12hr mode, bit 5 is the

AM/PM bit with logic 1 being PM. In the 24hr mode, bit

5 is the 20hr bit (20hr to 23hr). The CENT bit, bit 7 of

the Months register, can be written by the user. This bit

changes its state when the years counter transitions

from 99 to 00.

ister at address 0212h. It is important that the user sets

the EHSS bit accordingly while setting the Sample Rate

register. Writing a sample rate of 0000h results in a

sample rate = 0001h, causing the DS1923 to log the

temperature either every minute or every second

depending upon the state of the EHSS bit.

The calendar logic is designed to automatically com-

pensate for leap years. For every year value that is

either 00 or a multiple of 4, the device adds a 29th of

February. This works correctly up to (but not including)

the year 2100.

RTC Registers Bitmap

ADDRESS

0200h

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

0

10 Seconds

10 Minutes

Single Seconds

0201h

Single Minutes

Single Hours

20 Hour

AM/PM

0202h

0

12/24

10 Hour

0203h

0204h

0205h

0

10 Date

Single Date

Single Months

Single Years

CENT

0

10 Months

10 Years

Note: During a mission, there is only read access to these registers. Bit cells marked “0” always read 0 and cannot be written to 1.

Sample Rate Register Bitmap

ADDRESS

0206h

BIT 7

BIT 6

BIT 5

BIT 4

Sample Rate Low

Sample Rate High

BIT 3

BIT 2

BIT 1

BIT 0

0207h

0

Note: During a mission, there is only read access to these registers. Bit cells marked “0” always read 0 and cannot be written to 1.

______________________________________________________________________________________ 17

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

Because the temperature alarm threshold is only one

Temperature Conversion

The DS1923’s temperature range begins at -20°C and

ends at +85°C. Temperature values are represented as

an 8-bit or 16-bit unsigned binary number with a resolu-

tion of 0.5°C in 8-bit mode and 0.0625°C in 16-bit

mode.

byte, the resolution or temperature increment is limited to

0.5°C. The TALM value must be converted into hexadec-

imal format before it can be written to one of the

Temperature Alarm Threshold registers (Low Alarm

address 0208h; High Alarm address 0209h).

Independent of the conversion mode (8-bit or 16-bit),

only the most significant byte of a temperature conver-

sion is used to determine whether an alarm is generated.

The higher temperature byte TRH is always valid. In

16-bit mode, only the three highest bits of the lower

byte TRL are valid. The five lower bits all read 0. TRL is

undefined if the device is in 8-bit temperature mode. An

out-of-range temperature reading is indicated as 00h or

0000h when too cold and FFh or FFE0h when too hot.

DS1923

Humidity Conversion

In addition to temperature, the DS1923 can log humidi-

ty data in an 8-bit or 16-bit format. Humidity values are

represented as 8-bit or 16-bit unsigned binary numbers

with a resolution of 0.64%RH in the 8-bit mode and

0.04%RH in the 16-bit mode.

With TRH and TRL representing the decimal equivalent

of a temperature reading, the temperature value is cal-

culated as:

The DS1923 reads data from its humidity sensor when-

ever a Forced Conversion command is executed (see

the Memory and Control Function Commands section)

or during a mission if the device is set up to log humidi-

ty data. Regardless of its setup, the DS1923 always

reads 16 bits from the humidity sensor. The result of the

latest humidity reading is found at address 020Eh (low

byte) and 020Fh (high byte). The most significant bit

read from the humidity sensor can always be found as

H11 at address 020Fh. Due to the 12-bit digital output

of the humidity sensor, the lower 4 bits in 16-bit format

are undefined.

ϑ(°C) = TRH/2 - 41 + TRL/512 (16-bit mode,

TLFS = 1, see address 0213h)

ϑ(°C) = TRH/2 - 41 (8-bit mode, TLFS = 0,

see address 0213h)

This equation is valid for converting temperature read-

ings stored in the data-log memory as well as for data

read from the Latest Temperature Conversion Result

register.

To specify the temperature alarm thresholds, the previ-

ous equations are resolved to:

TALM = 2 x ϑ(°C) + 82

Latest Temperature Conversion Result Register Bitmap

ADDRESS

020Ch

BIT 7

T2

BIT 6

T1

BIT 5

T0

BIT 4

0

BIT 3

0

BIT 2

0

BIT 1

0

BIT 0

0

BYTE

TRL

020Dh

T10

T9

T8

T7

T6

T5

T4

T3

TRH

Table 1. Temperature Conversion Examples

TRH

TRL

MODE

ꢀ(°C)

HEX

54h

17h

54h

17h

DECIMAL

HEX

DECIMAL

8-Bit

84

23

84

23

—

0

1.0

-29.5

16-Bit

00h

60h

1.000

96

-29.3125

Table 2. Temperature Alarm Threshold Examples

TALM

ꢀ(°C)

HEX

85h

3Eh

DECIMAL

133

25.5

-10.0

62

18 ______________________________________________________________________________________

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

DS1923

Latest Humidity Conversion Result Register Bitmap

ADDRESS

020Eh

BIT 7

H3

BIT 6

H2

BIT 5

H1

BIT 4

H0

BIT 3

X

BIT 2

X

BIT 1

X

BIT 0

X

BYTE

HRL

020Fh

H11

H10

H9

H8

H7

H6

H5

H4

HRH

During a mission, if humidity logging is enabled, the

HRH byte (H11 to H4) is always recorded. The HRL

byte is only recorded if the DS1923 is set up for 16-bit

humidity logging. The logging mode (8-bit or 16-bit) is

selected through the HLFS bit at the Mission Control

register, address 0213h.

With HRH and HRL representing the decimal equivalent

of a humidity reading, the actual humidity is calculated

according to the algorithms shown in the table below.

16-BIT MODE, HLFS = 1

8-BIT MODE, HLFS = 0

(N/A)

IVAL = (HRH x 256 + HRL)/16

Round IVAL down to the nearest integer; this eliminates the

undefined 4 bits of HRL.

ADVAL = IVAL x 5.02/4096

ADVAL = HRH x 5.02/256

HUMIDITY(%RH) = (ADVAL - 0.958)/0.0307

The result is a raw humidity reading that needs to be

corrected to achieve the specified accuracy. See the

Software Correction Algorithm for Humidity section for

further details.

mode (8-bit or 16-bit), only the most significant byte of a

humidity conversion is used to determine whether an

alarm is generated. The alarm thresholds are applied to

the raw humidity readings. Therefore, if software correc-

tion is used, the effect of the software correction is to be

reversed before calculating a humidity alarm threshold.

For example, let the desired alarm threshold be 60%RH.

The 60% threshold may correspond to a raw reading of

65%RH (i.e., before correction). To set a 60%RH (after

correction) threshold, the HALM value then needs to be

calculated for 65%RH.

To specify the humidity alarm thresholds, the equation

needs to be resolved to:

ADVAL = HUMIDITY(%RH) x 0.0307 + 0.958

HALM = ADVAL x 256/5.02

Round HALM to the nearest integer.

The HALM value needs to be converted into hexadeci-

mal before it can be written to one of the Humidity Alarm

Threshold registers (Low Alarm address 020Ah; High

Alarm address 020Bh). Independent of the conversion

These examples do not include the effects of software

correction.

Table 3. Humidity Conversion Examples

HRH

HRL

MODE

HUMIDITY (%RH)

HEX

B5h

67h

B5h

67h

DECIMAL

181

HEX

ꢀ

DECIMAL

8-bit

ꢀ

12

48

84.41

34.59

84.89

34.70

8-bit

103

ꢀ

16-bit

181

C0h

30h

103

Table 4. Humidity Alarm Threshold Examples

HALM

HUMIDITY (%RH)

HEX

97h

58h

DECIMAL

151

65

25

88

______________________________________________________________________________________ 19

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

Temperature Sensor Control Register Bitmap

ADDRESS

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

0210h

0

ETHA

ETLA

Note: During a mission, there is only read access to this register. Bits 2 to 7 have no function. They always read 0 and cannot be written to 1.

Humidity Sensor Control Register Bitmap

DS1923

ADDRESS

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

0211h

1

EHHA

EHLA

Note: During a mission, there is only read access to this register. Bits 2 to 7 have no function. They always read 1 and cannot be written to 0.

RTC Control Register Bitmap

ADDRESS

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

0212h

0

EHSS

EOSC

Note: During a mission, there is only read access to this register. Bits 2 to 7 have no function. They always read 0 and cannot be written to 1.

alarm signaling is enabled. The bits EHLA and EHHA

that enable the humidity alarm are located in the

Humidity Sensor Control register. The corresponding

alarm flags HLF and HHF are found in the Alarm Status

register at address 0214h.

Temperature Sensor Alarm

The DS1923 has two Temperature Alarm Threshold

registers (address 0208h, 0209h) to store values that

determine whether a critical temperature has been

reached. A temperature alarm is generated if the

device measures an alarming temperature and the

alarm signaling is enabled. The bits ETLA and ETHA

that enable the temperature alarm are located in the

Temperature Sensor Control register. The temperature

alarm flags TLF and THF are found in the Alarm Status

register at address 0214h.

Bit 1: Enable Humidity High Alarm (EHHA). This bit

controls whether, during a mission, the humidity high

alarm flag (HHF) can be set, if a value from the humidi-

ty sensor is equal to or higher than the value in the

Humidity High Alarm Threshold register. If EHHA is 1,

humidity high alarms are enabled. If EHHA is 0, humidi-

ty high alarms are not generated.

Bit 1: Enable Temperature High Alarm (ETHA). This

bit controls whether, during a mission, the temperature

high alarm flag (THF) can be set, if a temperature con-

version results in a value equal to or higher than the

value in the Temperature High Alarm Threshold register.

If ETHA is 1, temperature high alarms are enabled. If

ETHA is 0, temperature high alarms are not generated.

Bit 0: Enable Humidity Low Alarm (EHLA). This bit

controls whether, during a mission, the humidity low

alarm flag (HLF) can be set, if a value from the humidity

sensor is equal to or lower than the value in the

Humidity Low Alarm Threshold register. If EHLA is 1,

humidity low alarms are enabled. If EHLA is 0, humidity

low alarms are not generated.

Bit 0: Enable Temperature Low Alarm (ETLA). This

bit controls whether, during a mission, the temperature

low alarm flag (TLF) can be set, if a temperature con-

version results in a value equal to or lower than the

value in the Temperature Low Alarm Threshold register.

If ETLA is 1, temperature low alarms are enabled. If

ETLA is 0, temperature low alarms are not generated.

RTC Control

To minimize the power consumption of a DS1923, the

RTC oscillator should be turned off when the device is

not in use. The oscillator on/off bit is located in the RTC

Control register. This register also includes the EHSS

bit, which determines whether the sample rate is speci-

fied in seconds or minutes.

Humidity Alarm

The DS1923 has two Humidity Alarm Threshold regis-

ters (address 020Ah, 020Bh) to store values that deter-

mine whether humidity readings can generate an

alarm. Such an alarm is generated if the humidity data

read from the sensor qualifies for an alarm and the

Bit 1: Enable High-Speed Sample (EHSS). This bit

controls the speed of the sample rate counter. When set

to logic 0, the sample rate is specified in minutes. When

set to logic 1, the sample rate is specified in seconds.

20 ______________________________________________________________________________________

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

DS1923

Bit 0: Enable Oscillator (EOSC). This bit controls the

ning, overwriting previously collected data. If this bit is

0, the logging and conversions stop once the data-log

memory is full. However, the RTC continues to run and

the MIP bit remains set until the Stop Mission command

is performed.

crystal oscillator of the RTC. When set to logic 1, the

oscillator starts. When written to logic 0, the oscillator

stops and the device is in a low-power data-retention

mode. This bit must be 1 for normal operation. A

Forced Conversion or Start Mission command automati-

cally starts the RTC by changing the EOSC bit to

logic 1.

Bit 3: Humidity Logging Format Selection (HLFS).

This bit specifies the format used to store humidity

readings in the data-log memory. If this bit is 0, the

data is stored in 8-bit format. If this bit is 1, the 16-bit

format is used (higher resolution). With 16-bit format,

the most significant byte is stored at the lower address.

Mission Control

The DS1923 is set up for its operation by writing appro-

priate data to its special function registers, which are

located in the two register pages. The settings in the

Mission Control register determine whether temperature

and/or humidity is logged, which format (8 or 16 bits)

applies, and whether old data can be overwritten by

new data once the data-log memory is full. An addition-

al control bit can be set to tell the DS1923 to wait with

logging data until a temperature alarm is encountered.

Bit 2: Temperature Logging Format Selection

(TLFS). This bit specifies the format used to store tem-

perature readings in the data-log memory. If this bit is

0, the data is stored in 8-bit format. If this bit is 1, the

16-bit format is used (higher resolution). With 16-bit for-

mat, the most significant byte is stored at the lower

address.

Bit 1: Enable Humidity Logging (EHL). To set up the

DS1923 for a humidity-logging mission, this bit must be

set to logic 1. If temperature and humidity logging are

enabled, the recorded humidity values begin at

address 2000h (TLFS = HLFS) or 1A00h (TLFS = 0;

HLFS = 1) or 2400h (TLFS = 1; HLFS = 0). If only

humidity logging is enabled, the recorded values are

stored starting at address 1000h. Since humidity data

has little scientific value without knowing the tempera-

ture, typically both humidity and temperature logging

are enabled (i.e., ETL and EHL are set to 1).

Bit 5: Start Mission Upon Temperature Alarm

(SUTA). This bit specifies whether a mission begins

immediately (includes delayed start) or if a temperature

alarm is required to start the mission. If this bit is 1, the

device performs an 8-bit temperature conversion at the

selected sample rate and begins with data logging only

if an alarming temperature (high alarm or low alarm)

was found. The first logged temperature is when the

alarm occurred. However, the Mission Samples

Counter does not increment. The start upon tempera-

ture alarm function is only available if temperature log-

ging is enabled (ETL = 1).

Bit 0: Enable Temperature Logging (ETL). To set up

the device for a temperature-logging mission, this bit

must be set to logic 1. To successfully start a mission,

ETL or EHL must be 1. If temperature logging is

enabled, the recorded temperature values are always

stored starting at address 1000h.

Bit 4: Rollover Control (RO). This bit controls whether,

during a mission, the data-log memory is overwritten

with new data or whether data logging is stopped once

the data-log memory is full. Setting this bit to 1 enables

the rollover and data logging continues at the begin-

Mission Control Register Bitmap

ADDRESS

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

0213h

1

SUTA

RO

HLFS

TLFS

EHL

ETL

Note: During a mission, there is only read access to this register. Bits 6 and 7 have no function. They always read 1 and cannot be written to 0.

______________________________________________________________________________________ 21

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

Alarm Status Register Bitmap

ADDRESS

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

0214h

BOR

1

HHF

HLF

THF

TLF

Note: There is only read access to this register. Bits 4 to 6 have no function. They always read 1. All five alarm status bits are cleared

simultaneously when the Clear Memory command is invoked. See the Memory and Control Function Commands section for details.

DS1923

General Status Register Bitmap

ADDRESS

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

0215h

1

0

WFTA

MEMCLR

0

MIP

0

Note: There is only read access to this register. Bits 0, 2, 5, 6, and 7 have no function.

during a mission revealing a temperature equal to or

lower than the value in the Temperature Low Alarm reg-

ister. A forced conversion can affect the TLF bit. This

bit can also be set with the initial alarm in the SUTA = 1

mode.

Alarm Status

The fastest way to determine whether a programmed

temperature or humidity threshold was exceeded during

a mission is through reading the Alarm Status register.

In a networked environment that contains multiple

DS1923 iButtons, the devices that encountered an alarm

can quickly be identified by means of the Conditional

Search ROM command (see the 1-Wire ROM Function

Commands section). The humidity and temperature

alarm only occurs if enabled (see the Temperature

Sensor Alarm and Humidity Alarm sections). The BOR

alarm is always enabled.

General Status

The information in the General Status register tells the

host computer whether a mission-related command

was executed successfully. Individual status bits indi-

cate whether the DS1923 is performing a mission, wait-

ing for a temperature alarm to trigger the logging of

data or whether the data from the latest mission has

been cleared.

Bit 7: Battery-On Reset Alarm (BOR). If this bit reads

1, the device has performed a power-on reset. This

indicates that the device has experienced a shock big

enough to interrupt the internal battery power supply.

The device can still appear functional, but it has lost its

factory calibration. Any data found in the data-log

memory should be disregarded.

Bit 4: Waiting for Temperature Alarm (WFTA). If this

bit reads 1, the mission start upon temperature alarm

was selected and the Start Mission command was suc-

cessfully executed, but the device has not yet experi-

enced the temperature alarm. This bit is cleared after a

temperature alarm event, but is not affected by the

Clear Memory command. Once set, WFTA remains set

if a mission is stopped before a temperature alarm

occurs. To clear WFTA manually before starting a new

mission, set the high temperature alarm (address

0209h) to -40°C and perform a forced conversion.

Bit 3: Humidity High Alarm Flag (HHF). If this bit

reads 1, there was at least one humidity reading during

a mission revealing a value equal to or higher than the

value in the Humidity High Alarm register. A forced

conversion can affect the HHF bit.

Bit 2: Humidity Low Alarm Flag (HLF). If this bit reads

1, there was at least one humidity reading during a mis-

sion revealing a value equal to or lower than the value

in the Humidity Low Alarm register. A forced conversion

can affect the HLF bit.

Bit 3: Memory Cleared (MEMCLR). If this bit reads 1,

the Mission Timestamp, Mission Samples Counter, and

all the alarm flags of the Alarm Status register have

been cleared in preparation of a new mission. Executing

the Clear Memory command clears these memory sec-

tions. The MEMCLR bit returns to 0 as soon as a new

mission is started by using the Start Mission command.

The memory must be cleared for a mission to start.

Bit 1: Temperature High Alarm Flag (THF). If this bit

reads 1, there was at least one temperature conversion

during a mission revealing a temperature equal to or

higher than the value in the Temperature High Alarm

register. A forced conversion can affect the THF bit.

This bit can also be set with the initial alarm in the

SUTA = 1 mode.

Bit 1: Mission in Progress (MIP). If this bit reads 1, the

device has been set up for a mission and this mission is

still in progress. The MIP bit returns from logic 1 to logic

0 when a mission is ended. See the Start Mission [with

Password] [CCh] and Stop Mission [with Password]

[33h] sections.

Bit 0: Temperature Low Alarm Flag (TLF). If this bit

reads 1, there was at least one temperature conversion

22 ______________________________________________________________________________________

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

DS1923

Mission Start Delay Counter Register Bitmap

ADDRESS

0216h

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

Delay Low Byte

0217h

Delay Center Byte

Delay High Byte

0218h

Note: During a mission, there is only read access to this register.

Mission Timestamp Register Bitmap

ADDRESS

0219h

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

0

10 Seconds

10 Minutes

Single Seconds

021Ah

Single Minutes

Single Hours

20 Hours

AM/PM

021Bh

0

12/24

10 Hours

021Ch

021Dh

021Eh

0

10 Date

Single Date

Single Months

Single Years

CENT

0

10 Months

10 Years

Note: There is only read access to this register.

Mission Samples Counter Register Bitmap

ADDRESS

0220h

BIT 7

BIT 6

BIT 5

BIT 4

Low Byte

BIT 3

BIT 2

BIT 1

BIT 0

0221h

Center Byte

High Byte

0222h

Note: There is only read access to this register. Note that when both the internal temperature and humidity logging are enabled, the

two log readings are counted as one event in the Mission Samples Counter and Device Samples Counter.

Mission Start Delay

The content of the Mission Start Delay Counter register

tells how many minutes must expire from the time a mis-

sion was started until the first measurement of the mis-

sion takes place (SUTA = 0) or until the device starts

testing the temperature for a temperature alarm (SUTA =

1). The Mission Start Delay register is stored as an

unsigned 24-bit integer number. The maximum delay is

16,777,215min, equivalent to 11,650 days or roughly

31yr. If the start delay is nonzero and the SUTA bit is set

to 1, first the delay must expire before the device starts

testing for temperature alarms to begin logging data.

Mission Timestamp

The Mission Timestamp register indicates the date and time

of the first temperature and humidity sample of the mission.

There is only read access to the Mission Timestamp register.

Mission Progress Indicator

Depending on settings in the Mission Control register

(address 0213h), the DS1923 logs temperature and/or

humidity in 8-bit or 16-bit format. The description of the

ETL and EHL bit explains where the device stores data

in its data-log memory. The Mission Samples Counter

register together with the starting address and the log-

ging format (8 or 16 bits) provide the information to iden-

tify valid blocks of data that have been gathered during

the current (MIP = 1) or latest mission (MIP = 0). See the

Data-Log Memory Usage section for an illustration. Note

that when SUTA = 1, the Mission Samples Counter does

not increment when the first sample is logged.

For a typical mission, the Mission Start Delay is 0. If a

mission is too long for a single DS1923 to store all read-

ings at the selected sample rate, one can use several

devices and set the Mission Start Delay for the second

device to start recording as soon as the memory of the

first device is full, and so on. The RO bit in the Mission

Control register (address 0213h) must be set to 0 to

prevent overwriting of collected data once the data-log

memory is full.

The number read from the Mission Samples Counter indi-

cates how often the DS1923 woke up during a mission to

measure temperature and/or humidity. The number for-

mat is 24-bit unsigned integer. The Mission Samples

Counter is reset through the Clear Memory command.

______________________________________________________________________________________ 23

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

Device Samples Counter Register Bitmap

ADDRESS

0223h

BIT 7

BIT 6

BIT 5

BIT 4

Low Byte

BIT 3

BIT 2

BIT 1

BIT 0

0224h

Center Byte

High Byte

0225h

Note: There is only read access to this register.

DS1923

Device Configuration Register Bitmap

ADDRESS

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

PART

0

1

0

1

0

1

0

1

0

DS2422

DS1923

DS1922L

DS1922T

DS1922E

0226h

Note: There is only read access to this register.

Password Control Register Bitmap

ADDRESS

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

0227h

EPW

Note: During a mission, there is only read access to this register.

Other Indicators

The Device Samples Counter register is similar to the

Mission Samples Counter register. During a mission this

counter increments whenever the DS1923 wakes up to

measure and log data and when the device is testing

for a temperature alarm in Start Mission Upon

Temperature Alarm mode. Between missions, the

counter increments whenever the Forced Conversion

command is executed. This way the Device Samples

Counter register functions like a gas gauge for the bat-

tery that powers the iButton.

Security by Password

The DS1923 is designed to use two passwords that

control read access and full access. Reading from or

writing to the scratchpad as well as the Forced

Conversion command does not require a password.

The password must be transmitted immediately after

the command code of the memory or control function. If

password checking is enabled, the password transmit-

ted is compared to the passwords stored in the device.

The data pattern stored in the Password Control regis-

ter determines whether password checking is enabled.

The Device Samples Counter register is reset to zero

when the iButton is assembled. The number format is

24-bit unsigned integer. The maximum number that can

be represented in this format is 16,777,215. Due to the

calibration and tests at the factory, new devices can

have a count value of up to 35,000. The typical value is

well below 10,000.

To enable password checking, the EPW bits need to

form a binary pattern of 10101010 (AAh). The default

pattern of EPW is different from AAh. If the EPW pattern

is different from AAh, any pattern is accepted as long

as it has a length of exactly 64 bits. Once enabled,

changing the passwords and disabling password

checking requires the knowledge of the current full-

access password.

The code in the Device Configuration register allows the

master to distinguish between the DS2422 chip and dif-

ferent versions of the DS1922 iButtons. The Device

Configuration Register Bitmap table shows the codes

assigned to the various devices.

24 ______________________________________________________________________________________

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

DS1923

Read-Access Password Register Bitmap

ADDRESS

0228h

0229h

…

BIT 7

RP7

BIT 6

RP6

BIT 5

RP5

BIT 4

RP4

BIT 3

RP3

BIT 2

RP2

BIT 1

RP1

BIT 0

RP0

RP15

RP14

RP13

RP12

RP11

RP10

RP9

RP8

…

022Eh

022Fh

RP55

RP63

RP54

RP62

RP53

RP61

RP52

RP60

RP51

RP59

RP50

RP58

RP49

RP57

RP48

RP56

Note: There is only write access to this register. Attempting to read the password reports all zeros. The password cannot be

changed while a mission is in progress.

Full-Access Password Register Bitmap

ADDRESS

0230h

0231h

…

BIT 7

FP7

BIT 6

FP6

BIT 5

FP5

BIT 4

FP4

BIT 3

FP3

BIT 2

FP2

BIT 1

FP1

BIT 0

FP0

FP15

FP14

FP13

FP12

FP11

FP10

FP9

FP8

…

0236h

0237h

FP55

FP63

FP54

FP62

FP53

FP61

FP52

FP60

FP51

FP59

FP50

FP58

FP49

FP57

FP48

FP56

Note: There is only write access to this register. Attempting to read the password reports all zeros. The password cannot be

changed while a mission is in progress.

Before enabling password checking, passwords for

read-only access as well as for full access

(read/write/control) must be written to the password

registers. Setting up a password or enabling/dis-

abling the password checking is done in the same

way as writing data to a memory location; only the

address is different. Since they are located in the

same memory page, both passwords can be rede-

fined at the same time.

The Full Access Password must be transmitted exactly

in the sequence FP0, FP1…FP62, FP63. It affects the

commands Read Memory with CRC, Copy Scratchpad,

Clear Memory, Start Mission, and Stop Mission. The

DS1923 executes the command only if the password

transmitted by the master was correct or if password

checking is not enabled.

Due to the special behavior of the write-access logic,

the Password Control register and both passwords

must be written at the same time. When setting up new

passwords, always verify (read back) the scratchpad

before sending the Copy Scratchpad command. After a

new password is successfully copied from the scratch-

pad to its memory location, erase the scratchpad by fill-

ing it with new data (Write Scratchpad command).

Otherwise, a copy of the passwords remains in the

scratchpad for public read access.

The Read Access Password must be transmitted exact-

ly in the sequence RP0, RP1…RP62, RP63. This pass-

word only applies to the Read Memory with CRC

command. The DS1923 delivers the requested data

only if the password transmitted by the master was cor-

rect or if password checking is not enabled.

______________________________________________________________________________________ 25

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

If alarm signaling is desired, the temperature alarm

Data-Log Memory Usage

and/or humidity alarm low and high thresholds must be

defined. See the Temperature Conversion section for

information on how to convert a temperature value into

the binary code to be written to the threshold registers.

See the Humidity Conversion section for information on

determining the thresholds for the humidity alarm. In

addition, the temperature alarm and/or humidity alarm

must be enabled for the low and/or high threshold. This

makes the device respond to a Conditional Search

ROM command (see the1-Wire ROM Function

Commands section), provided that an alarming condi-

tion has been encountered.

Once set up for a mission, the DS1923 logs the temper-

ature and/or humidity measurements at equidistant time

points entry after entry in its data-log memory. The

data-log memory can store 8192 entries in 8-bit format

or 4096 entries in 16-bit format (Figure 7a). If tempera-

ture as well as humidity are logged, both in the same

format, the memory is split into two equal sections that

can store 4096 8-bit entries or 2048 16-bit entries

(Figure 7b). If the device is set up to log data in differ-

ent formats, e. g., temperature in 8-bit and humidity in

16-bit format, the memory is split into blocks of different

size, accommodating 2560 entries for either data

source (Figure 7c). In this case, the upper 256 bytes

are not used. In 16-bit format, the higher 8 bits of an

entry are stored at the lower address. Knowing the

starting time point (Mission Timestamp) and the interval

between temperature measurements, one can recon-

struct the time and date of each measurement.

DS1923

The setting of the RO bit (rollover enable) and sample

rate depends on the duration of the mission and the

monitoring requirements. If the most recently logged

data is important, the rollover should be enabled (RO =

1). Otherwise one should estimate the duration of the

mission in minutes and divide the number by 8192 (sin-

gle channel 8-bit format) or 4096 (single channel 16-bit

format, two channels 8-bit format) or 2048 (two channels

16-bit format) or 2560 (two channels, one 8-bit and one

16-bit format) to calculate the value of the sample rate

(number of minutes between conversions). If the esti-

mated duration of a mission is 10 days (= 14400min), for

example, then the 8192-byte capacity of the data-log

memory would be sufficient to store a new 8-bit value

every 1.8min (110s). If the data-log memory of the

DS1923 is not large enough to store all readings, one

can use several devices and set the Mission Start Delay

to values that make the second device start logging as

soon as the memory of the first device is full, and so on.

The RO-bit needs to be set to 0 to disable rollover that

would otherwise overwrite the logged data.

There are two alternatives to the way the DS1923

behaves after the data-log memory is filled with data.

The user can program the device to either stop any fur-

ther recording (disable rollover) or overwrite the previ-

ously recorded data (enable rollover), one entry at a

time, starting again at the beginning of the respective

memory section. The contents of the Mission Samples

Counter in conjunction with the sample rate and the

Mission Timestamp allow reconstructing the time

points of all values stored in the data-log memory. This

gives the exact history over time for the most recent

measurements taken. Earlier measurements cannot be

reconstructed.

Missioning

After the RO bit and the Mission Start Delay are set, the

sample rate must be written to the Sample Rate regis-

ter. The sample rate can be any value from 1 to 16,383,

coded as an unsigned 14-bit binary number. The

fastest sample rate is one sample per second (EHSS =

1, sample rate = 0001h) and the slowest is one sample

every 273.05hr (EHSS = 0, sample rate = 3FFFh). To

get one sample every 6min, for example, the sample

rate value must be set to 6 (EHSS = 0) or 360 decimal

(equivalent to 0168h at EHSS = 1).

The typical task of the DS1923 iButton is recording tem-

perature and/or humidity. Before the device can per-

form this function, it needs to be set up properly. This

procedure is called missioning.

First, the DS1923 must have its RTC set to a valid time

and date. This reference time can be the local time, or,

when used inside of a mobile unit, UTC (also called

GMT, Greenwich Mean Time), or any other time stan-

dard that was agreed upon. The RTC oscillator must be

running (EOSC = 1). The memory assigned to store the

Mission Timestamp, Mission Samples Counter, and

alarm flags must be cleared using the Clear Memory

command. To enable the device for a mission, at least

one of the enable logging bits (ETL, EHL) must be set

to 1. These are general settings that must be made in

any case, regardless of the type of object to be moni-

tored and the duration of the mission.

If there is a risk of unauthorized access to the DS1923

or manipulation of data, one should define passwords

for read access and full access. Before the passwords

become effective, their use must be enabled. See the

Security by Password section for more details.

26 ______________________________________________________________________________________

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

DS1923

ETL = 1; EHL = 0 OR ETL = 0; EHL = 1

TLFS = HLFS = 0

ETL = 1; EHL = 0 OR ETL = 0; EHL = 1

TLFS = HLFS = 1

1000h

8192

1000h

4096

8-BIT ENTRIES

TEMPERATURE

OR

16-BIT ENTRIES

TEMPERATURE

OR

WITH 16-BIT FORMAT, THE MOST SIGNIFICANT

BYTE IS STORED AT THE LOWER ADDRESS.

HUMIDITY DATA

2FFFh

Figure 7a. 1-Channel Logging

ETL = EHL = 1

TLFS = HLFS = 0

TLFS = HLFS = 1

1000h

TEMPERATURE

2048

4096

8-BIT ENTRIES

16-BIT ENTRIES

1FFFh

2000h

1FFFh

2000h

WITH 16-BIT FORMAT, THE MOST SIGNIFICANT

BYTE IS STORED AT THE LOWER ADDRESS.

HUMIDITY DATA

4096

HUMIDITY DATA

2048

8-BIT ENTRIES

16-BIT ENTRIES

2FFFh

Figure 7b. 2-Channel Logging, Equal Resolution

ETL = EHL = 1

TLFS = 0; HLFS = 1

TLFS = 1; HLFS = 0

1000h

TEMPERATURE

2560

8-BIT ENTRIES

TEMPERATURE

2560

19FFh

16-BIT ENTRIES

1A00h

23FFh

HUMIDITY DATA

2560

16-BIT ENTRIES

WITH 16-BIT FORMAT, THE MOST SIGNIFICANT

BYTE IS STORED AT THE LOWER ADDRESS.

2400h

HUMIDITY DATA

2560

8-BIT ENTRIES

2DFFh

2E00h

(NOT USED)

2E00h

(NOT USED)

2FFFh

Figure 7c. 2-Channel Logging, Different Resolution

______________________________________________________________________________________ 27

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

The last step to begin a mission is to issue the Start

Mission command. As soon as it has received this com-

mand, the DS1923 sets the MIP flag and clears the

MEMCLR flag. With the immediate/delayed start mode

(SUTA = 0), after as many minutes as specified by the

Mission Start Delay are over, the device wakes up,

copies the current date and time to the Mission

Timestamp register, and logs the first entry of the mis-

sion. This increments both the Mission Samples

Counter and Device Samples Counter. All subsequent

log entries are made as specified by the value in the

Sample Rate register and the EHSS bit.

at any time, e.g., to watch the progress of a mission.

Attempts to read the passwords read 00h bytes instead

of the data that is stored in the password registers.

Memory Access

Address Registers and Transfer Status

Because of the serial data transfer, the DS1923

employs three address registers called TA1, TA2, and

E/S (Figure 8). Registers TA1 and TA2 must be loaded

with the target address to which the data is written or

from which data is sent to the master upon a read com-

mand. Register E/S acts like a byte counter and trans-

fer status register. It is used to verify data integrity with

write commands. Therefore, the master only has read

access to this register. The lower 5 bits of the E/S regis-

ter indicate the address of the last byte that has been

written to the scratchpad. This address is called ending

offset. The DS1923 requires that the ending offset is

always 1Fh for a Copy Scratchpad to function. Bit 5

of the E/S register, called PF or partial byte flag, is set if

the number of data bits sent by the master is not an

integer multiple of 8. Bit 6 is always a 0. Note that the

lowest 5 bits of the target address also determine the

address within the scratchpad, where intermediate

storage of data begins. This address is called byte off-

set. If the target address for a Write Scratchpad com-

mand is 13Ch, for example, the scratchpad stores

incoming data beginning at the byte offset 1Ch and is

full after only 4 bytes. The corresponding ending offset

in this example is 1Fh. For best economy of speed and

DS1923

If the start upon temperature alarm mode is chosen

(SUTA = 1) and temperature logging is enabled (ETL =

1), the DS1923 first waits until the start delay is over.

Then the device wakes up in intervals as specified by

the sample rate and EHSS bit and measures the tem-

perature. This increments the Device Samples Counter

register only. The first sample of the mission is logged

when the temperature alarm occurred. However, the

Mission Samples Counter does not increment. One

sample period later the Mission Timestamp register is

set. From then on, both the Mission Samples Counter

and Device Samples Counter registers increment at the

same time. All subsequent log entries are made as

specified by the value in the Sample Rate register and

the EHSS bit.

The general-purpose memory operates independently of

the other memory sections and is not write protected

during a mission. All the DS1923’s memory can be read

BIT NUMBER

7

6

5

4

3

2

1

0

TARGET ADDRESS (TA1)

T7

T6

T5

T4

T3

T2

T1

T0

TARGET ADDRESS (TA2)

T15

AA

T14

0

T13

PF

T12

E4

T11

E3

T10

E2

T9

E1

T8

E0

ENDING ADDRESS WITH

DATA STATUS (E/S)

(READ ONLY)

Figure 8. Address Registers

28 ______________________________________________________________________________________

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

DS1923

efficiency, the target address for writing should point to

Memory and Control

Function Commands

the beginning of a page, i.e., the byte offset is 0. Thus,

the full 32-byte capacity of the scratchpad is available,

resulting also in the ending offset of 1Fh. The ending

offset together with the PF flag are a means to support

the master checking the data integrity after a Write

Scratchpad command. The highest valued bit of the

E/S register, called authorization accepted (AA), indi-

cates that a valid Copy Scratchpad command for the

scratchpad has been received and executed. Writing

data to the scratchpad clears this flag.

Figure 9 shows the protocols necessary for accessing

the memory and the special function registers of the

DS1923. An example on how to use these and other

functions to set up the DS1923 for a mission is included

in the Mission Example: Prepare and Start a New

Mission section. The communication between the mas-

ter and the DS1923 takes place either at standard

speed (default, OD = 0) or at overdrive speed (OD =

1). If not explicitly set into the overdrive mode, the

DS1923 assumes standard speed. Internal memory

access during a mission has priority over external

access through the 1-Wire interface. This affects sever-

al commands in this section. See the Memory Access

Conflicts section for details and solutions.

Writing with Verification

To write data to the DS1923, the scratchpad must be

used as intermediate storage. First, the master issues

the Write Scratchpad command to specify the desired

target address, followed by the data to be written to the

scratchpad. In the next step, the master sends the

Read Scratchpad command to read the scratchpad

and to verify data integrity. As preamble to the scratch-

pad data, the DS1923 sends the requested target

address TA1 and TA2 and the contents of the E/S

Register. If the PF flag is set, data did not arrive cor-

rectly in the scratchpad. The master does not need to

continue reading; it can start a new trial to write data to

the scratchpad. Similarly, a set AA flag indicates that

the Write Scratchpad command was not recognized by

the device. If everything went correctly, both flags are

cleared and the ending offset indicates the address of

the last byte written to the scratchpad. Now the master

can continue verifying every data bit. After the master

has verified the data, it must send the Copy Scratchpad

command. This command must be followed exactly by

the data of the three address registers TA1, TA2, and

E/S, as the master has read them verifying the scratch-

pad. As soon as the DS1923 has received these bytes,

it copies the data to the requested location beginning

at the target address.

Write Scratchpad [0Fh]

After issuing the Write Scratchpad command, the mas-

ter must first provide the 2-byte target address, fol-

lowed by the data to be written to the scratchpad. The

data is written to the scratchpad starting at the byte off-

set T[4:0]. The master must send as many bytes as are

needed to reach the ending offset of 1Fh. If a data byte

is incomplete, its content is ignored and the partial byte

flag PF is set.

When executing the Write Scratchpad command, the

CRC generator inside the DS1923 calculates a CRC of

the entire data stream, starting at the command code

and ending at the last data byte sent by the master

(Figure 15). This CRC is generated using the CRC-16

polynomial by first clearing the CRC generator and then

shifting in the command code (0Fh) of the Write

Scratchpad command, the target addresses TA1 and

TA2 as supplied by the master, and all the data bytes.

If the ending offset is 11111b, the master can send 16

read time slots and receive the inverted CRC-16 gener-

ated by the DS1923.

Note that both register pages are write protected dur-

ing a mission. Although the Write Scratchpad command

works normally at any time, the subsequent copy

scratchpad to a register page fails during a mission.

______________________________________________________________________________________ 29

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

progress, write attempts to the register pages are not

Read Scratchpad [AAh]

This command is used to verify scratchpad data and

target address. After issuing the Read Scratchpad

command, the master begins reading. The first 2 bytes

are the target address. The next byte is the ending off-

set/data status byte (E/S) followed by the scratchpad

data beginning at the byte offset T[4:0], as shown in

Figure 8. The master can continue reading data until

the end of the scratchpad after which it receives an

inverted CRC-16 of the command code, target

addresses TA1 and TA2, the E/S byte, and the scratch-

pad data starting at the target address. After the CRC

is read, the bus master reads logic 1s from the DS1923

until a reset pulse is issued.

successful. The AA bit remaining at 0 indicates this.

Read Memory with [Password

and] CRC [69h]

The Read Memory with CRC command is the general

function to read from the device. This command gener-

ates and transmits a 16-bit CRC following the last data

byte of a memory page.

DS1923

After having sent the command code of the Read

Memory with CRC command, the bus master sends a

2-byte address that indicates a starting byte location.

Next, the master must transmit one of the 64-bit pass-

words. If passwords are enabled and the transmitted

password does not match one of the stored passwords,

the Read Memory with CRC command fails. The device

stops communicating and waits for a reset pulse. If the

password was correct or if passwords were not

enabled, the master reads data from the DS1923

beginning from the starting address and continuing

until the end of a 32-byte page is reached. At that point

the bus master sends 16 additional read-data time slots

and receives the inverted 16-bit CRC. With subsequent

read-data time slots the master receives data starting at

the beginning of the next memory page followed again

by the CRC for that page. This sequence continues

until the bus master resets the device. When trying to

read the passwords or memory areas that are marked

as “reserved,” the DS1923 transmits 00h or FFh bytes,

respectively. The CRC at the end of a 32-byte memory

page is based on the data as it was transmitted.

Copy Scratchpad [with Password] [99h]

This command is used to copy data from the scratch-

pad to the writable memory sections. After issuing the

Copy Scratchpad command, the master must provide a

3-byte authorization pattern, which can be obtained by

reading the scratchpad for verification. This pattern

must exactly match the data contained in the three

address registers (TA1, TA2, E/S, in that order). Next,

the master must transmit the 64-bit full access pass-

word. If passwords are enabled and the transmitted

password is different from the stored full access pass-

word, the Copy Scratchpad command fails. The device

stops communicating and waits for a reset pulse. If the

password was correct or if passwords were not

enabled, the device tests the 3-byte authorization code.

If the authorization code pattern matches, the AA flag is

set and the copy begins. A pattern of alternating 1s and

0s is transmitted after the data has been copied until

the master issues a reset pulse. While the copy is in

progress, any attempt to reset the part is ignored. Copy

typically takes 2μs per byte.

With the initial pass through the Read Memory with

CRC flow, the 16-bit CRC value is the result of shifting

the command byte into the cleared CRC generator fol-

lowed by the 2 address bytes and the contents of the

data memory. Subsequent passes through the Read

Memory with CRC flow generate a 16-bit CRC that is

the result of clearing the CRC generator and then shift-

ing in the contents of the data memory page. After the

16-bit CRC of the last page is read, the bus master

receives logic 1s from the DS1923 until a reset pulse is

issued. The Read Memory with CRC command

sequence can be ended at any point by issuing a reset

pulse.

The data to be copied is determined by the three

address registers. The scratchpad data from the begin-

ning offset through the ending offset are copied, start-

ing at the target address. The AA flag remains at logic

1 until it is cleared by the next Write Scratchpad com-

mand. With suitable password, the copy scratchpad

always functions for the 16 pages of data memory and

the 2 pages of calibration memory. While a mission is in

30 ______________________________________________________________________________________

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

DS1923

MASTER Tx MEMORY OR

CONTROL FUNCTION COMMAND

FROM ROM FUNCTIONS

FLOWCHART (FIGURE 11)

99h

TO FIGURE 9b

0Fh

AAh

N

COPY SCRATCHPAD

[WITH PW]

WRITE SCRATCHPAD?

READ SCRATCHPAD?

Y

MASTER Tx

TA1 [T7:T0]

MASTER Rx

TA1 [T7:T0]

MASTER Tx

TA1 [T7:T0], TA2 [T15:T8]

AUTHORIZATION

CODE

MASTER Tx

TA2 [T15:T8]

MASTER Rx

TA2 [T15:T8]

MASTER Tx

E/S BYTE

DS1923 SETS

SCRATCHPAD OFFSET = [T4:T0]

AND CLEARS (PF, AA)

MASTER Rx ENDING OFFSET

WITH DATA STATUS

(E/S)

MASTER Tx

64 BITS [PASSWORD]

N

PASSWORD

ACCEPTED?

MASTER Tx DATA BYTE

TO SCRATCHPAD OFFSET

DS1923 SETS

SCRATCHPAD OFFSET = [T4:T0]

Y

DS1923

INCREMENTS

SCRATCHPAD

OFFSET

DS1923 SETS [E4:E0] =

SCRATCHPAD OFFSET

DS1923

INCREMENTS

SCRATCHPAD

OFFSET

MASTER Rx DATA BYTE FROM

SCRATCHPAD OFFSET

AUTHORIZATION

CODE MATCH?

Y

MASTER Tx RESET?

N

MASTER Tx RESET?

N

AA = 1

DS1923 COPIES SCRATCHPAD

DATA TO MEMORY

N

Y

SCRATCHPAD

OFFSET = 11111b?

N

SCRATCHPAD

OFFSET = 11111b?

PARTIAL

BYTE WRITTEN?

Y

MASTER Rx "1"s

N

COPYING

FINISHED

MASTER Rx CRC-16 OF

COMMAND, ADDRESS DATA,

E/S BYTE, AND DATA STARTING

AT THE TARGET ADDRESS

N

MASTER Tx RESET?

N

Y

MASTER Tx RESET?

Y

PF = 1

DS1923 Tx "0"

MASTER Rx CRC-16 OF

COMMAND, ADDRESS DATA

Y

MASTER Tx RESET?

Y

MASTER Tx RESET?

N

Y

MASTER Tx RESET?

MASTER Rx "1"s

N

DS1923 Tx "1"

MASTER Rx "1"s

N

MASTER Tx RESET?

Y

FROM FIGURE 9b

TO ROM FUNCTIONS

FLOWCHART (FIGURE 11)

Figure 9a. Memory/Control Function Flowchart

______________________________________________________________________________________ 31

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

69h

96h

FROM FIGURE 9a

TO FIGURE 9c

55h

N

READ MEMORY [WITH

PW] AND CRC

CLEAR MEMORY

[WITH PW]

FORCED CONVERSION?

Y

DS1923

MASTER Tx

TA1 [T7:T0], TA2 [T15:T8]

64 BITS [PASSWORD]

FFh DUMMY BYTE

MASTER Tx

64 BITS [PASSWORD]

MASTER Tx

FFh DUMMY BYTE

Y

MISSION IN

PROGRESS?

DECISION MADE

BY DS1923

N

Y

PASSWORD

ACCEPTED?

PASSWORD

ACCEPTED?

DS1923 PERFORMS A

TEMPERATURE CONVERSION

Y

DECISION MADE

BY MASTER

DS1923 SETS

MEMORY ADDRESS = [T15:T0]

DS1923 COPIES RESULT TO

ADDRESS 020C/Dh

MISSION IN

PROGRESS?

N

MASTER Rx DATA BYTE FROM

MEMORY ADDRESS

DS1923 PERFORMS A

HUMIDITY CONVERSION

DS1923 CLEARS

MISSION TIMESTAMP,

MISSION SAMPLES COUNTER,

ALARM FLAGS

DS1923

INCREMENTS

ADDRESS

DS1923 COPIES RESULT TO

ADDRESS 020E/Fh

Y

MASTER Tx RESET?

N

COUNTER

DS1923 SETS

MEMCLR = 1

N

MASTER Tx RESET?

Y

N

END OF PAGE?

Y

N

MASTER Tx RESET?

Y

MASTER Rx CRC-16 OF

COMMAND, ADDRESS, DATA

(1ST PASS); CRC-16 OF DATA

(SUBSEQUENT PASSES)

N

MASTER Tx RESET

CRC OK?

Y

N

END OF MEMORY?

Y

MASTER Rx "1"s

MASTER Tx RESET?

Y

TO FIGURE 9a

FROM FIGURE 9c

Figure 9b. Memory/Control Function Flowchart (continued)

32 ______________________________________________________________________________________

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

DS1923

CCh

START MISSION

[WITH PW]

33h

FROM FIGURE 9b

N

STOP MISSION

[WITH PW]

MISSION START

DELAY PROCESS

Y

MASTER Tx

64 BITS [PASSWORD]

Y

START DELAY

COUNTER = 0?

MASTER Tx

FFh DUMMY BYTE

MASTER Tx

FFh DUMMY BYTE

N

DS1923 WAITS FOR 1 MINUTE

N

Y

N

PASSWORD

ACCEPTED?

PASSWORD

ACCEPTED?

DS1923 DECREMENTS

START DELAY COUNTER

Y

N

MISSION IN

PROGRESS?

MISSION IN

PROGRESS?

SUTA = 1?

Y

N

Y

DS1923 SETS WFTA = 1

DS1923 SETS

MIP = 0,

WFTA = 0

MEMCLR = 1?

Y

DS1923 WAITS ONE

SAMPLE PERIOD

DS1923 SETS

MIP = 1,

MEMCLR = 0

N

Y

MASTER Tx RESET?

Y

MIP = 0?

N

DS1923 INITIATES MISSION

START DELAY PROCESS

DS1923 PERFORMS 8-BIT

TEMPERATURE CONVERSION

N

TEMPERATURE

ALARM?

MASTER Tx RESET?

Y

THE MISSION

DS1923 SETS WFTA = 0

AND LOGS FIRST SAMPLE

SAMPLES COUNTER

DOES NOT

INCREMENT

DS1923 WAITS ONE

SAMPLE PERIOD

IF SUTA = 1,

THIS IS THE

SECOND SAMPLE.

DS1923 COPIES RTC DATA TO

MISSION TIMESTAMP REGISTER

DS1923 STARTS LOGGING

TAKING FIRST SAMPLE

END OF PROCESS

TO FIGURE 9b

Figure 9c. Memory/Control Function Flowchart (continued)

______________________________________________________________________________________ 33

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

Clear Memory [with Password] [96h]

The Clear Memory with Password command is used to

prepare the device for another mission. This command

is only executed if no mission is in progress. After the

command code, the master must transmit the 64-bit

full-access password followed by an FFh dummy byte.

If passwords are enabled and the transmitted pass-

word is different from the stored full access password

or a mission is in progress, the Clear Memory com-

mand fails. The device stops communicating and waits

for a reset pulse. If the password was correct or if pass-

words were not enabled, the device clears the Mission

Timestamp register, Mission Samples Counter register,

and all alarm flags of the Alarm Status register. After

these cells are cleared, the MEMCLR bit of the General

Status register reads 1 to indicate the successful exe-

cution of the Clear Memory with Password command.

Clearing of the data-log memory is not necessary

because the Mission Samples Counter indicates how

many entries in the data-log memory are valid.

Start Mission [with Password] [CCh]

The DS1923 uses a control function command to start a

mission. A new mission can only be started if the previ-

ous mission has been ended and the memory has been

cleared. After the command code, the master must

transmit the 64-bit full access password followed by an

FFh dummy byte. If passwords are enabled and the

transmitted password is different from the stored full-

access password or a mission is in progress, the Start

Mission command fails. The device stops communicat-

ing and waits for a reset pulse. If the password was

correct or if passwords were not enabled, the device

starts a mission. If SUTA = 0, the sampling begins as

soon as the Mission Start Delay is over. If SUTA = 1, the

first sample is written to the data-log memory at the

time the temperature alarm occurred. However, the

Mission Samples Counter does not increment. One

sample period later, the Mission Timestamp register is

set and the regular sampling and logging begins. While

the device is waiting for a temperature alarm to occur,

the WFTA flag in the General Status register reads 1.

During a mission there is only read access to the regis-

ter pages.

DS1923

Forced Conversion [55h]

The Forced Conversion command can be used to mea-

sure the temperature and humidity without starting a

mission. After the command code, the master must

send one FFh byte to get the conversion started. The

conversion result is found as a 16-bit value in the Latest

Temperature Conversion Result and Latest Humidity

Conversion Result registers. This command is only exe-

cuted if no mission is in progress (MIP = 0). It cannot

be interrupted and takes maximum 666ms to complete.

During this time memory access through the 1-Wire

interface is blocked. The device behaves the same way

as during a mission when the sampling interferes with a

memory/control function command. See the Memory

Access Conflicts section for details.

Stop Mission [with Password] [33h]

The DS1923 uses a control function command to stop a

mission. Only a mission that is in progress can be

stopped. After the command code, the master must

transmit the 64-bit full access password followed by a

FFh dummy byte. If passwords are enabled and the

transmitted password is different from the stored full-

access password or a mission is not in progress, the

Stop Mission command fails. The device stops commu-

nicating and waits for a reset pulse. If the password

was correct or if passwords were not enabled, the

device clears the MIP bit in the General Status register

and restores write access to the register pages. The

WFTA bit is not cleared. See the description of the gen-

eral status register for a method to clear the WFTA bit.

34 ______________________________________________________________________________________

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

DS1923

device is waiting for a temperature alarm. Table 5

Memory Access Conflicts

explains how the remaining five commands are affect-

While a mission is in progress or while the device is

ed by internal activity, how to detect this interference,

and how to work around it.

waiting for a temperature alarm to start a mission, peri-

odically a temperature and/or humidity sample is taken

and logged. This “internal activity” has priority over

1-Wire communication. As a consequence, device-spe-

cific commands (excluding ROM function commands

and 1-Wire reset) do not perform properly when internal

and “external” activities interfere with each other. Not

affected are the commands Start Mission, Forced

Conversion, and Clear Memory, because they are not

applicable while a mission is in progress or while the

The interference is more likely to be seen with a high-

sample rate (one sample every second) and with high-

resolution logging, which can last up to 666ms when

both temperature and humidity are recorded. With

lower sample rates, interference may hardly be visible

at all. In any case, when writing driver software it is

important to know about the possibility of interference

and to take measures to work around it.

Table 5. Memory Access Conflicts and Solutions

COMMAND

INDICATION OF INTERFERENCE

SOLUTION

Wait 0.5s, 1-Wire reset, address the device, repeat

Write Scratchpad with the same data, and check the

validity of the CRC-16 at the end of the command

flow. Alternatively, use Read Scratchpad to verify

data integrity.

The CRC-16 at the end of the command flow reads

FFFFh.

Write Scratchpad

The data read changes to FFh bytes or all bytes

received are FFh, including the CRC at the end of

the command flow.

Wait 0.5s, 1-Wire reset, address the device, repeat

Read Scratchpad, and check the validity of the

CRC-16 at the end of the command flow.

Read Scratchpad

Copy Scratchpad

Wait 0.5s, 1-Wire reset, address the device, issue

Read Scratchpad, and check the AA bit of the E/S

byte. If the AA bit is set, Copy Scratchpad was

successful.

The device behaves as if the authorization code or

password was not valid or as if the copy function

would not end.

The data read changes to all FFh bytes or all bytes

received are FFh, including the CRC at the end of

the command flow, despite a valid password.

Wait 0.5s, 1-Wire reset, address the device, repeat

Read Memory with CRC, and check the validity of

the CRC-16 at the end of the memory page.

Read Memory with

CRC

Wait 0.5s, 1-Wire reset, address the device, and

repeat Stop Mission. Perform a 1-Wire reset, address

the device, read the General Status register at

address 0215h, and check the MIP bit. If the MIP bit

is 0, Stop Mission was successful.

The General Status register at address 0215h reads

FFh or the MIP bit is 1 while bits 0, 2, and 5 are 0.

Stop Mission

______________________________________________________________________________________ 35

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

The value of the pullup resistor primarily depends on

1-Wire Bus System

the network size and load conditions. The DS1923

requires a pullup resistor of maximum 2.2kΩ at any

speed.

The 1-Wire bus is a system that has a single bus mas-

ter and one or more slaves. In all instances the DS1923

is a slave device. The bus master is typically a micro-

controller. The discussion of this bus system is broken

down into three topics: hardware configuration, trans-

action sequence, and 1-Wire signaling (signal types

and timing). The 1-Wire protocol defines bus transac-

tions in terms of the bus state during specific time slots

that are initiated on the falling edge of sync pulses from

the bus master.

The idle state for the 1-Wire bus is high. If for any rea-

son a transaction needs to be suspended, the bus

must be left in the idle state if the transaction is to

resume. If this does not occur and the bus is left low for

more than 16μs (overdrive speed) or more than 120μs

(standard speed), one or more devices on the bus may

be reset. Note that the DS1923 does not quite meet the

full 16μs maximum low time of the normal 1-Wire bus

overdrive timing. With the DS1923 the bus must be left

low for no longer than 12μs at overdrive to ensure that

no DS1923 on the 1-Wire bus performs a reset. The

DS1923 communicates properly when used in conjunc-

tion with a DS2480B or DS2490 1-Wire driver and

adapters that are based on these driver chips.

DS1923

Hardware Configuration

The 1-Wire bus has only a single line by definition; it is

important that each device on the bus be able to drive

it at the appropriate time. To facilitate this, each device

attached to the 1-Wire bus must have open-drain or

three-state outputs. The 1-Wire port of the DS1923 is

open drain with an internal circuit equivalent to that

shown in Figure 10.

Transaction Sequence

The protocol for accessing the DS1923 through the

1-Wire port is as follows:

A multidrop bus consists of a 1-Wire bus with multiple

slaves attached. At standard speed the 1-Wire bus has

a maximum data rate of 16.3kbps. The speed can be

boosted to 142kbps by activating the overdrive mode.

The DS1923 is not guaranteed to be fully compliant to

the iButton standard. Its maximum data rate in standard

speed is 15.4kbps and 125kbps in overdrive speed.

• Initialization

• ROM Function Command

• Memory/Control Function Command

• Transaction/Data

V

PUP

BUS MASTER

DS1923 1-Wire PORT

R

PUP

DATA

Rx

Tx

Rx

I

L

Tx

Rx = RECEIVE

Tx = TRANSMIT

OPEN-DRAIN

PORT PIN

100Ω MOSFET

Figure 10. Hardware Configuration

36 ______________________________________________________________________________________

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

DS1923

numbers of all slave devices. For each bit of the regis-

tration number, starting with the least significant bit, the

Initialization

All transactions on the 1-Wire bus begin with an initial-

bus master issues a triplet of time slots. On the first slot,

each slave device participating in the search outputs

the true value of its registration number bit. On the sec-

ond slot, each slave device participating in the search

outputs the complemented value of its registration num-

ber bit. On the third slot, the master writes the true

value of the bit to be selected. All slave devices that do

not match the bit written by the master stop participat-

ing in the search. If both of the read bits are zero, the

master knows that slave devices exist with both states

of the bit. By choosing which state to write, the bus

master branches in the ROM code tree. After one com-

plete pass, the bus master knows the registration num-

ber of a single device. Additional passes identify the

registration numbers of the remaining devices. Refer to

Application Note 187: 1-Wire Search Algorithm for a

detailed discussion, including an example.

ization sequence. The initialization sequence consists

of a reset pulse transmitted by the bus master followed

by presence pulse(s) transmitted by the slave(s). The

presence pulse lets the bus master know that the

DS1923 is on the bus and is ready to operate. For more

details, see the 1-Wire Signaling section.

1-Wire ROM Function Commands

Once the bus master has detected a presence, it can

issue one of the eight ROM function commands that the

DS1923 supports. All ROM function commands are 8

bits long. A list of these commands follows (see the

flowchart in Figure 11).

Read ROM [33h]

This command allows the bus master to read the

DS1923’s 8-bit family code, unique 48-bit serial number,

and 8-bit CRC. This command can only be used if there

is a single slave on the bus. If more than one slave is pre-

sent on the bus, a data collision occurs when all slaves

try to transmit at the same time (open drain produces a

wired-AND result). The resultant family code and 48-bit

serial number results in a mismatch of the CRC.

Conditional Search ROM [ECh]

The Conditional Search ROM command operates simi-

larly to the Search ROM command except that only

those devices that fulfill certain conditions participate in

the search. This function provides an efficient means

for the bus master to identify devices on a multidrop

system that have to signal an important event. After

each pass of the conditional search that successfully

determined the 64-bit ROM code for a specific device

on the multidrop bus, that particular device can be indi-

vidually accessed as if a Match ROM had been issued,

since all other devices have dropped out of the search

process and are waiting for a reset pulse.

Match ROM [55h]

The Match ROM command, followed by a 64-bit ROM

sequence, allows the bus master to address a specific

DS1923 on a multidrop bus. Only the DS1923 that exact-

ly matches the 64-bit ROM sequence responds to the fol-

lowing memory function command. All other slaves wait

for a reset pulse. This command can be used with a sin-

gle device or multiple devices on the bus.

The DS1923 responds to the Conditional Search ROM

command if one of the five alarm flags of the Alarm

Status register (address 0214h) reads 1. The humidity

and temperature alarm only occurs if enabled (see the

Temperature Sensor Alarm and Humidity Alarm sec-

tions). The BOR alarm is always enabled. The first

alarm that occurs makes the device respond to the

Conditional Search ROM command.

Search ROM [F0h]

When a system is initially brought up, the bus master

might not know the number of devices on the 1-Wire

bus or their registration numbers. By taking advantage

of the wired-AND property of the bus, the master can

use a process of elimination to identify the registration

______________________________________________________________________________________ 37

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

ROM command sets the DS1923 in the overdrive mode

Skip ROM [CCh]

This command can save time in a single-drop bus sys-

tem by allowing the bus master to access the memory

functions without providing the 64-bit ROM code. For

example, if more than one slave is present on the bus

and a read command is issued following the Skip ROM

command, data collision occurs on the bus as multiple

slaves transmit simultaneously (open-drain pulldowns

produce a wired-AND result).

(OD = 1). All communication following this command

must occur at overdrive speed until a reset pulse of

minimum 690μs duration resets all devices on the bus

to standard speed (OD = 0).

When issued on a multidrop bus, this command sets all

overdrive-supporting devices into overdrive mode. To

subsequently address a specific overdrive-supporting

device, a reset pulse at overdrive speed must be

issued followed by a Match ROM or Search ROM com-

mand sequence. This speeds up the time for the

search process. If more than one slave supporting

overdrive is present on the bus and the Overdrive-Skip

ROM command is followed by a read command, data

collision occurs on the bus as multiple slaves transmit

simultaneously (open-drain pulldowns produce a wired-

AND result).

DS1923

Resume [A5h]

The DS1923 must be accessed several times before a

mission starts. In a multidrop environment this means

that the 64-bit ROM code after a Match ROM command

must be repeated for every access. To maximize the

data throughput in a multidrop environment, the Resume

command was implemented. This command checks the

status of the RC bit and, if it is set, directly transfers con-

trol to the memory/control functions, similar to a Skip

ROM command. The only way to set the RC bit is

through successfully executing the Match ROM, Search

ROM, or Overdrive-Match ROM command. Once the RC

bit is set, the device can repeatedly be accessed

through the Resume command. Accessing another

device on the bus clears the RC bit, preventing two or

more devices from simultaneously responding to the

Resume command.

Overdrive-Match ROM [69h]

The Overdrive-Match ROM command followed by a

64-bit ROM sequence transmitted at overdrive speed

allows the bus master to address a specific DS1923 on

a multidrop bus and to simultaneously set it in overdrive

mode. Only the DS1923 that exactly matches the 64-bit

ROM sequence responds to the subsequent

memory/control function command. Slaves already in

overdrive mode from a previous Overdrive-Skip ROM or

successful Overdrive-Match ROM command remain in

overdrive mode. All overdrive-capable slaves return to

standard speed at the next reset pulse of minimum

690μs duration. The Overdrive-Match ROM command

can be used with a single or multiple devices on the

bus.

Overdrive-Skip ROM [3Ch]

On a single-drop bus this command can save time by

allowing the bus master to access the memory/control

functions without providing the 64-bit ROM code. Unlike

the normal Skip ROM command, the Overdrive-Skip

38 ______________________________________________________________________________________

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

DS1923

BUS MASTER Tx

RESET PULSE

FROM FIGURE 11b

FROM MEMORY/CONTROL

FUNCTION FLOWCHART (FIGURE 9)

OD

N

OD = 0

RESET PULSE?

Y

BUS MASTER Tx ROM

FUNCTION COMMAND

DS1923 Tx

PRESENCE PULSE

33h

READ ROM

COMMAND?

55h

MATCH ROM

COMMAND?

F0h

SEARCH ROM

COMMAND?

ECh

TO FIGURE 11b

N

CONDITIONAL SEARCH

COMMAND?

Y

RC = 0

N

CONDITION

MET?

Y

DS1923 Tx BIT 0

MASTER Tx BIT 0

DS1923 Tx BIT 0

MASTER Tx BIT 0

DS1923 Tx

FAMILY CODE

(1 BYTE)

MASTER Tx BIT 0

BIT 0 MATCH?

N

BIT 0 MATCH?

Y

BIT 0 MATCH?

Y

DS1923 Tx BIT 1

MASTER Tx BIT 1

DS1923 Tx BIT 1

MASTER Tx BIT 1

DS1923 Tx

SERIAL NUMBER

(6 BYTES)

MASTER Tx BIT 1

N

BIT 1 MATCH?

Y

BIT 1 MATCH?

Y

BIT 1 MATCH?

Y

DS1923 Tx BIT 63

MASTER Tx BIT 63

DS1923 Tx BIT 63

MASTER Tx BIT 63

DS1923 Tx

CRC BYTE

MASTER Tx BIT 63

BIT 63 MATCH?

N

BIT 63 MATCH?

Y

RC = 1

TO FIGURE 11b

FROM FIGURE 11b

TO MEMORY/CONTROL

FUNCTION FLOWCHART (FIGURE 9)

Figure 11a. ROM Functions Flowchart

______________________________________________________________________________________ 39

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

TO FIGURE 11a

DS1923

CCh

SKIP ROM

COMMAND?

A5h

RESUME

COMMAND?

3Ch

OVERDRIVE-

SKIP ROM?

69h

OVERDRIVE-

MATCH ROM?

FROM FIGURE 11a

N

Y

RC = 0

RC = 0; OD = 1

N

RC = 1?

Y

MASTER Tx

RESET?

MASTER Tx BIT 0

BIT 0 MATCH?

N

(SEE NOTE)

OD = 0

Y

N

MASTER Tx

RESET?

N

Y

MASTER Tx BIT 1

(SEE NOTE)

OD = 0

BIT 1 MATCH?

Y

MASTER Tx BIT 63

BIT 63 MATCH?

(SEE NOTE)

OD = 0

Y

RC = 1

FROM FIGURE 11a

TO FIGURE 11a

NOTE: THE OD FLAG REMAINS AT 1 IF THE DEVICE WAS ALREADY AT OVERDRIVE SPEED BEFORE THE OVERDRIVE-MATCH ROM COMMAND WAS ISSUED.

Figure 11b. ROM Functions Flowchart (continued)

40 ______________________________________________________________________________________

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

DS1923

DS1923 is in overdrive mode and t

is no longer

RSTL

1-Wire Signaling

than 80μs, the device remains in overdrive mode.

The DS1923 requires strict protocols to ensure data

integrity. The protocol consists of four types of signaling

on one line: reset sequence with reset pulse and pres-

ence pulse, write-zero, write-one, and read-data. Except

for the presence pulse, the bus master initiates all these

signals. The DS1923 can communicate at two different

speeds: standard speed and overdrive speed. If not

explicitly set into the overdrive mode, the DS1923 com-

municates at standard speed. While in overdrive mode

the fast timing applies to all waveforms.

After the bus master has released the line, it goes into

receive mode (Rx). Now the 1-Wire bus is pulled to

PUP

V

through the pullup resistor or, in the case of a

DS2480B driver, through active circuitry. When the

threshold V is crossed, the DS1923 waits for t

TH

PDH

and then transmits a presence pulse by pulling the line

low for t . To detect a presence pulse, the master

PDL

must test the logical state of the 1-Wire line at t

.

MSP

The t

window must be at least the sum of

RSTH

t

, t

, and t

. Immediately after

RECMIN

PDHMAX PDLMAX

RSTH

To get from idle to active, the voltage on the 1-Wire line

is expired, the DS1923 is ready for data commu-

needs to fall from V

below the threshold V . To get

TL

PUP

nication. In a mixed population network, t

should

RSTH

from active to idle, the voltage needs to rise from

past the threshold V . The time it takes for the

be extended to minimum 480μs at standard speed and

48μs at overdrive speed to accommodate other 1-Wire

devices.

V

ILMAX

TH

voltage to make this rise is seen in Figure 12 as “ε” and

its duration depends on the pullup resistor (R ) used

PUP

and the capacitance of the 1-Wire network attached.

Read/Write Time Slots

Data communication with the DS1923 takes place in

time slots that carry a single bit each. Write time slots

transport data from bus master to slave. Read time slots

transfer data from slave to master. The definitions of the

write and read time slots are illustrated in Figure 13.

The voltage V

is relevant for the DS1923 when

ILMAX

determining a logical level, not triggering any events.

The initialization sequence required to begin any com-

munication with the DS1923 is shown in Figure 12. A

reset pulse followed by a presence pulse indicates the

DS1923 is ready to receive data, given the correct ROM

and memory function command. If the bus master uses

slew-rate control on the falling edge, it must pull down

All communication begins with the master pulling the

data line low. As the voltage on the 1-Wire line falls

below the threshold V , the DS1923 starts its internal

TL

timing generator that determines when the data line is

sampled during a write time slot and how long data is

valid during a read time slot.

the line for t

RSTL

+ t to compensate for the edge. A

F

RSTL

t

duration of 690μs or longer exits the overdrive

mode, returning the device to standard speed. If the

MASTER Tx "RESET PULSE"

MASTER Rx "PRESENCE PULSE"

ε

t

MSP

V

PUP

V

IHMASTER

V

TH

V

TL

V

ILMAX

0V

t

PDH

t

REC

RSTL

PDL

t

F

t

RSTH

RESISTOR

MASTER

DS1923

Figure 12. Initialization Procedure: Reset and Presence Pulse

______________________________________________________________________________________ 41

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

Master-to-Slave

sources can also result in signal glitching. A glitch dur-

For a write-one time slot, the voltage on the data line

ing the rising edge of a time slot can cause a slave

device to lose synchronization with the master and, as

a consequence, result in a Search ROM command

coming to a dead end or cause a device-specific func-

tion command to abort. For better performance in net-

work applications, the DS1923 uses a new 1-Wire

front-end, which makes it less sensitive to noise and

also reduces the magnitude of noise injected by the

slave device itself.

must have crossed the V threshold before the write-one

TH

low time t

is expired. For a write-zero time slot,

W1LMAX

the voltage on the data line must stay below the V

TH

threshold until the write-zero low time t

is expired.

W0LMIN

The voltage on the data line should not exceed V

ILMAX

window. After the V

DS1923

during the entire t

or t

W0L

W1L TH

threshold has been crossed, the DS1923 needs a recov-

ery time t before it is ready for the next time slot.

REC

The DS1923’s 1-Wire front-end differs from traditional

slave devices in four characteristics:

Slave-to-Master

A read-data time slot begins like a write-one time slot.

1) The falling edge of the presence pulse has a con-

trolled slew rate. This provides a better match to the

line impedance than a digitally switched transistor,

converting the high-frequency ringing known from

traditional devices into a smoother, low-bandwidth

transition. The slew-rate control is specified by the

The voltage on the data line must remain below V

TL

RL

until the read low time t

is expired. During the t

RL

window, when responding with a 0, the DS1923 starts

pulling the data line low; its internal timing generator

determines when this pulldown ends and the voltage

starts rising again. When responding with a 1, the

DS1923 does not hold the data line low at all, and the

parameter t

, which has different values for stan-

FPD

dard and overdrive speed.

voltage starts rising as soon as t is over.

RL

2) There is additional lowpass filtering in the circuit that

detects the falling edge at the beginning of a time

slot. This reduces the sensitivity to high-frequency

noise. This additional filtering does not apply at over-

drive speed.

The sum of t + δ (rise time) on one side and the inter-

RL

nal timing generator of the DS1923 on the other side

define the master sampling window (t

MSRMAX

the data line. For most reliable communication, t

to

MSRMIN

t

) in which the master must perform a read from

RL

should be as short as permissible and the master

should read close to but no later than t . After

3) There is a hysteresis at the low-to-high switching

MSRMAX

threshold V . If a negative glitch crosses V

but

TH

reading from the data line, the master must wait until

does not go below V

- V , it is not recognized

HY

TH

t

is expired. This guarantees sufficient recovery

REC

SLOT

(Figure 14, Case A). The hysteresis is effective at

any 1-Wire speed.

time t

slot.

for the DS1923 to get ready for the next time

4) There is a time window specified by the rising edge

hold-off time t

during which glitches are ignored,

Improved Network Behavior

(Switchpoint Hysteresis)

REH

even if they extend below V

- V

threshold

HY

TH

REH

(Figure 14, Case B, t

< t

). Deep voltage

GL

In a 1-Wire environment, line termination is possible

only during transients controlled by the bus master (1-

Wire driver). 1-Wire networks, therefore, are susceptible

to noise of various origins. Depending on the physical

size and topology of the network, reflections from end

points and branch points can add up or cancel each

other to some extent. Such reflections are visible as

glitches or ringing on the 1-Wire communication line.

Noise coupled onto the 1-Wire line from external

droops or glitches that appear late after crossing the

threshold and extend beyond the t window

V

TH

REH

cannot be filtered out and are taken as the begin-

ning of a new time slot (Figure 14, Case C, t

≥

GL

t ).

REH

Devices that have the parameters t , V , and t

FPD HY REH

specified in their electrical characteristics use the

improved 1-Wire front-end.

42 ______________________________________________________________________________________

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

DS1923

WRITE-ONE TIME SLOT

t

W1L

V

PUP

V

IHMASTER

V

TH

V

TL

V

ILMAX

0V

ε

t

F

t

SLOT

RESISTOR

MASTER

WRITE-ZERO TIME SLOT

t

W0L

V

PUP

V

IHMASTER

V

TH

V

TL

V

ILMAX

0V

ε

t

F

t

REC

t

SLOT

RESISTOR

MASTER

READ-DATA TIME SLOT

t

MSR

t

RL

V

PUP

V

IHMASTER

V

TH

MASTER

SAMPLING

WINDOW

V

TL

V

ILMAX

0V

δ

t

REC

F

t

SLOT

RESISTOR

MASTER

DS1923

Figure 13. Read/Write Timing Diagrams

______________________________________________________________________________________ 43

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

t

REH

t

REH

V

PUP

V

TH

V

HY

CASE A

CASE B

CASE C

DS1923

0V

t

GL

t

GL

Figure 14. Noise Suppression Scheme

16

15

2

POLYNOMIAL = X + X + X + 1

1ST

2ND

3RD

4TH

5TH

6TH

7TH

8TH

STAGE

0

1

2

3

4

5

6

7

X

9TH

STAGE

10TH

STAGE

11TH

STAGE

12TH

STAGE

13TH

STAGE

14TH

STAGE

15TH

STAGE

16TH

STAGE

8

9

10

11

12

13

14

15

16

CRC OUTPUT

X

INPUT DATA

Figure 15. CRC-16 Hardware Description and Polynomial

CRC, the 16-bit CRC is always communicated in the

inverted form. A CRC generator inside the DS1923

(Figure 15) calculates a new 16-bit CRC as shown in

the command flowchart of Figure 9. The bus master

compares the CRC value read from the device to the

one it calculates from the data and decides whether to

continue with an operation or to reread the portion of

the data with the CRC error. With the initial pass

through the Read Memory with CRC flowchart, the 16-

bit CRC value is the result of shifting the command byte

into the cleared CRC generator, followed by the 2

address bytes and the data bytes. The password is

excluded from the CRC calculation. Subsequent pass-

es through the Read Memory with CRC flowchart gen-

erate a 16-bit CRC that is the result of clearing the CRC

generator and then shifting in the data bytes.

CRC Generation

The DS1923 uses two types of CRCs. One CRC is an

8-bit type and is stored in the most significant byte of

the 64-bit ROM. The bus master can compute a CRC

value from the first 56 bits of the 64-bit ROM and com-

pare it to the value stored within the DS1923 to deter-

mine if the ROM data has been received error-free. The

equivalent polynomial function of this CRC is

8

5

4

X + X + X + 1. This 8-bit CRC is received in the true

(noninverted) form, and it is computed at the factory

and lasered into the ROM.

The other CRC is a 16-bit type, generated according to

the standardized CRC-16 polynomial function

16

15

2

X

+ X + X + 1. This CRC is used for error detec-

tion when reading register pages or the data-log mem-

ory using the Read Memory with CRC command and

for fast verification of a data transfer when writing to or

reading from the scratchpad. In contrast to the 8-bit

With the Write Scratchpad command, the CRC is gener-

ated by first clearing the CRC generator and then shift-

44 ______________________________________________________________________________________

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

DS1923

ing in the command code, the target addresses TA1

shifting in the command code, the target addresses

TA1 and TA2, the E/S byte, and the scratchpad data

starting at the target address. The DS1923 transmits

this CRC only if the reading continues through the end

of the scratchpad, regardless of the actual ending off-

set. For more information on generating CRC values,

refer to Application Note 27.

and TA2, and all the data bytes. The DS1923 transmits

this CRC only if the data bytes written to the scratchpad

include scratchpad ending offset 11111b. The data can

start at any location within the scratchpad.

With the Read Scratchpad command, the CRC is gen-

erated by first clearing the CRC generator and then

Command-Specific 1-Wire Communication Protocol—Legend

SYMBOL

RST

DESCRIPTION

1-Wire reset pulse generated by master.

PD

1-Wire presence pulse generated by slave.

Command and data to satisfy the ROM function protocol.

Command “Write Scratchpad.”

Select

WS

RS

Command “Read Scratchpad.”

CPS

Command “Copy Scratchpad with Password.”

Command “Read Memory with Password and CRC.”

Command “Clear Memory with Password.”

RMC

CM

FC

Command “Forced Conversion.”

SM

Command “Start Mission with Password.”

STP

Command “Stop Mission with Password.”

TA

Target Address TA1, TA2.

TA–E/S

<32 Bytes>

<Data>

FFh

Target Address TA1, TA2 with E/S byte.

Transfer of as many data bytes as are needed to reach the scratchpad offset 1Fh.

Transfer of as many data bytes as are needed to reach the end of a memory page.

Transfer as many bytes as are needed to reach the end of the data-log memory.

Transfer of 8 bytes that either represent a valid password or acceptable dummy data.

Transfer of 32 bytes.

Transfer of an undetermined amount of data.

Transmission of one FFh byte.

CRC-16

FF Loop

AA Loop

Transfer of an inverted CRC-16.

Indefinite loop where the master reads FF bytes.

Indefinite loop where the master reads AA bytes.

______________________________________________________________________________________ 45

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

Command-Specific 1-Wire Communication Protocol—Color Codes

Master-to-Slave Slave-to-Master

1-Wire Communication Examples

DS1923

Write Scratchpad, Reaching the End of the Scratchpad (Cannot Fail)

RST PD Select WS TA <Data to EOS> CRC-16 FF Loop

Read Scratchpad (Cannot Fail)

RST PD Select RS TA-E/S <Data to EOS> CRC-16 FF Loop

Copy Scratchpad with Password (Success)

RST PD Select CPS TA-E/S <PW/Dummy> AA Loop

Copy Scratchpad with Password (Fail TA-E/S or Password)

RST PD Select CPS TA-E/S <PW/Dummy> FF Loop

Read Memory with Password and CRC (Success)

RST PD Select RMC TA <PW/Dummy> <Data to EOP> CRC-16

<32 Bytes>

CRC-16 FF Loop

Loop

Read Memory with Password and CRC (Fail Password or Address)

RST PD Select RMC TA <PW/Dummy> FF Loop

Clear Memory with Password

RST PD Select CM <PW/Dummy> FFh FF Loop

To verify success, read the General Status register at address 0215h. If MEMCLR is 1, the command was

executed successfully.

46 ______________________________________________________________________________________

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

DS1923

1-Wire Communication Examples (continued)

Forced Conversion

RST PD Select FC FFh FF Loop

To read the result and to verify success, read the addresses 020Ch to 020Fh (results) and the Device Samples

Counter at address 0223h to 0225h. If the count has incremented, the command was executed successfully.

Start Mission with Password

RST PD Select SM <PW/Dummy> FFh FF Loop

To verify success, read the General Status register at address 0215h. If MIP is 1 and MEMCLR is 0, the command

was executed successfully.

Stop Mission with Password

RST PD Select STP <PW/Dummy> FFh FF Loop

To verify success, read the General Status register at address 0215h. If MIP is 0, the command was executed

successfully.

Step 1: Clear the data of the previous mission.

Mission Example: Prepare

and Start a New Mission

Assumption: The previous mission has been ended by

Step 2: Write the setup data to register page 1.

Step 3: Start the new mission.

using the Stop Mission command. Passwords are not

enabled. The device is a DS1923.

Step 1: Clear the data of the previous mission.

With only a single device connected to the bus master,

the communication of step 1 looks like this:

Starting a mission requires three steps:

MASTER MODE

DATA (LSB FIRST)

(Reset)

COMMENTS

Tx

Rx

Tx

Rx

Reset pulse

(Presence)

CCh

Presence pulse

Issue “Skip ROM” command

Issue “Clear Memory” command

Send dummy password

Send dummy byte

Reset pulse

96h

<8 FFh bytes>

FFh

(Reset)

(Presence)

Presence pulse

______________________________________________________________________________________ 47

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

Step 2: Write the setup data to register page 1.

• Alarm Controls (Response to Conditional Search ROM)

During the setup, the device needs to learn the follow-

ing information:

• General Mission Parameters (e.g., Channels to Log

and Logging Format, Rollover, Start Mode)

• Time and Date

• Sample Rate

• Mission Start Delay

The following data sets up the DS1923 for a mission

that logs temperature and humidity using 8-bit format

for both.

• Alarm Thresholds

DS1923

ADDRESS

0200h

0201h

0202h

0203h

0204h

0205h

0206h

0207h

0208h

0209h

020Ah

020Bh

020Ch

020Dh

020Eh

020Fh

0210h

0211h

0212h

0213h

0214h

0215h

0216h

0217h

0218h

DATA

00h

30h

15h

05h

04h

0Ah

00h

66h

7Ah

6Fh

9Eh

FFh

03h

FFh

01h

C3h

FFh

5Ah

00h

EXAMPLE VALUES

FUNCTION

15:30:00 hours

Time

15th of May in 2004

Date

Every 10 minutes (EHSS = 0)

Sample rate

10°C Low

20°C High

Temperature Alarm Thresholds

40%RH Low

70%RH High

Humidity Alarm Threshold, no software

correction used

(Don’t care)

Clock through read-only registers

Enable high and low alarm

Temperature Alarm Control

Humidity Alarm Control

On (enabled), EHSS = 0 (low sample rate)

Normal start; no rollover; 8-bit logging

RTC Oscillator Control, sample rate selection

General Mission Control

(Don’t care)

Clock through read-only registers

90 minutes

Mission Start Delay

48 ______________________________________________________________________________________

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

DS1923

With only a single device connected to the bus master,

the communication of step 2 looks like this:

MASTER MODE

DATA (LSB FIRST)

(Reset)

(Presence)

CCh

COMMENTS

Tx

Rx

Tx

Rx

Tx

Rx

Tx

Rx

Tx

Rx

Reset pulse

Presence pulse

Issue “Skip ROM” command

Issue “Write Scratchpad” command

TA1, beginning offset = 00h

TA2, address = 0200h

0Fh

00h

02h

<25 Data Bytes>

<7 FFh Bytes>

(Reset)

(Presence)

CCh

Write 25 bytes of data to scratchpad

Write through the end of the scratchpad

Reset pulse

Presence pulse

Issue “Skip ROM” command

Issue “Read Scratchpad” command

Read TA1, beginning offset = 00h

Read TA2, address = 0200h

Read E/S, ending offset = 1Fh, flags = 0h

Read scratchpad data and verify

Reset pulse

AAh

00h

02h

1Fh

<32 Data Bytes>

(Reset)

(Presence)

CCh

Presence pulse

Issue “Skip ROM” command

Issue “Copy Scratchpad” command

TA1

99h

00h

(AUTHORIZATION CODE)

02h

TA2

E/S

1Fh

<8 FFh Bytes>

(Reset)

(Presence)

Send dummy password

Reset pulse

Presence pulse

Step 3: Start the new mission.

If step 3 was successful, the MIP bit in the General

Status register is 1, the MEMCLR bit is 0, and the

Mission Start Delay counts down.

With only a single device connected to the bus master,

the communication of step 3 looks like this:

MASTER MODE

DATA (LSB FIRST)

(Reset)

COMMENTS

Tx

Rx

Tx

Rx

Reset pulse

(Presence)

CCh

Presence pulse

Issue “Skip ROM” command

Issue “Start Mission” command

Send dummy password

Send dummy byte

Reset pulse

CCh

<8 FFh Bytes>

FFh

(Reset)

(Presence)

Presence pulse

______________________________________________________________________________________ 49

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

The software correction algorithm requires two addition-

al values, which are not stored in the device. For the

DS1923 these values are Tr1 = 60°C and Offset = 41.

Software Correction Algorithm

for Temperature

The accuracy of high-resolution temperature conver-

sion results (forced conversion as well as temperature

logs) can be improved through a correction algorithm.

The data needed for this software correction is stored in

the calibration memory (memory page 18). It consists of

reference temperature (Tr) and conversion result (Tc)

for two different temperatures, as shown below. See the

Temperature Conversion section for the binary number

format.

The correction algorithm consists of two steps, prepara-

tion and execution. The preparation step first converts

temperature data from binary to decimal °C format.

Next, three coefficients A, B, and C are computed. In

the execution step, the temperature reading as deliv-

ered by the DS1923 is first converted from the low/high-

byte format (TcL, TcH) to °C (Tc) and then corrected to

Tcorr. Once step 1 is performed, the three coefficients

can be used repeatedly to correct any temperature

reading and temperature log of the same device.

DS1923

ADDRESS

0240h

0241h

0242h

0243h

0244h

0245h

0246h

0247h

DESIGNATOR

Tr2H

DESCRIPTION

Cold reference temperature, high-byte.

Tr2L

Cold reference temperature, low-byte.

Tc2H

Conversion result at cold reference temperature, high-byte.

Conversion result at cold reference temperature, low-byte.

Hot reference temperature, high-byte.

Tc2L

Tr3H

Tr3L

Hot reference temperature, low-byte.

Tc3H

Conversion result at hot reference temperature, high-byte.

Conversion result at hot reference temperature, low-byte.

Tc3L

Step 1: Preparation

Tr1 = 60

Offset = 41

Tr2 = Tr2H/2 + Tr2L/512 - Offset

Tr3 = Tr3H/2 + Tr3L/512 - Offset

Tc2 = Tc2H/2 + Tc2L/512 - Offset

Tc3 = Tc3H/2 + Tc3L/512 - Offset

Err2 = Tc2 - Tr2

(convert from binary to °C)

Err3 = Tc3 - Tr3

Err1 = Err2

2

B = (Tr2 - Tr1 ) x (Err3 - Err1)/[(Tr2 - Tr1 ) x (Tr3 - Tr1) + (Tr3 - Tr1 ) x (Tr1 - Tr2)]

2

A = B x (Tr1 - Tr2)/(Tr2 - Tr1 )

2

C = Err1 - A x Tr1 - B x Tr1

Step 2: Execution

Tc = TcH/2 + TcL/512 - Offset

(convert from binary to °C)

(the actual correction)

2

Tcorr = Tc - (A x Tc + B x Tc + C)

50 ______________________________________________________________________________________

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

DS1923

Numerical Temperature Correction Example

CONVERTED DATA FROM CALIBRATION MEMORY

ERROR VALUES

Tr2 = -10.1297°C

Err2 = 0.0672°C

Err3 = -0.1483°C

Err1 = Err2

Tr3 = 24.6483°C

Tc2 = -10.0625°C

Tc3 = 24.5°C

APPLICATION OF CORRECTION COEFFICIENTS

TO SAMPLE READING

RESULTING CORRECTION COEFFICIENTS

B = -0.008741

A = 0.000175/°C

C = -0.039332°C

Tc = 22.500000°C

Tcorr = 22.647275°C

Note: The software correction requires floating point arithmetic (24-bit or better). Suitable math libraries for microcontrollers are

found on various websites and are included in cross-compilers.

The correction algorithm consists of two steps: prepara-

Software Correction Algorithm

tion and execution. The preparation step first converts

for Humidity

humidity data from binary to decimal %RH format. Next,

The accuracy of humidity conversion results (forced

conversion as well as logged data) can be improved

through a correction algorithm. The data needed for

this software correction is stored in the calibration

memory (memory page 18). It consists of reference

humidity (Hr) and conversion result (Hc) for three differ-

ent humidity levels, as shown below. The data is taken

at 25°C.

three coefficients A, B, and C are computed. In the exe-

cution step the humidity reading as delivered by the

DS1923 (raw data) is first converted from the low/high-

byte format (HcL, HcH) to %RH (Hc) and then correct-

ed to Hcorr. Once step 1 is performed, the three

coefficients can be used repeatedly to correct any

humidity reading and humidity log of the same device.

ADDRESS

0248h

0249h

024Ah

024Bh

024Ch

024Dh

024Eh

024Fh

0250h

0251h

0252h

0253h

DESIGNATOR

Hr1H

DESCRIPTION

Low reference humidity, high byte.

Hr1L

Low reference humidity, low byte.

Hc1H

Hc1L

Conversion result at low reference humidity, high byte.

Conversion result at low reference humidity, low byte.

Medium reference humidity, high byte.

Hr2H

Hr2L

Medium reference humidity, low byte.

Hc2H

Hc2L

Conversion result at medium reference humidity, high byte.

Conversion result at medium reference humidity, low byte.

High reference humidity, high byte.

Hr3H

Hr3L

High reference humidity, low byte.

Hc3H

Hc3L

Conversion result at high reference humidity, high byte.

Conversion result at high reference humidity, low byte.

______________________________________________________________________________________ 51

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

Step 1: Preparation

For the humidity data in the calibration memory, the lower 4 bits of each low byte are set to 0. This simplifies the con-

version from the binary data format to raw %RH values to a one-line equation.

Hr1 = ((Hr1H x 256 + Hr1L) x 5.02/65536 - 0.958)/0.0307

Hr2 = ((Hr2H x 256 + Hr2L) x 5.02/65536 - 0.958)/0.0307

Hr3 = ((Hr3H x 256 + Hr3L) x 5.02/65536 - 0.958)/0.0307

Hc1 = ((Hc1H x 256 + Hc1L) x 5.02/65536 - 0.958)/0.0307

Hc2 = ((Hc2H x 256 + Hc2L) x 5.02/65536 - 0.958)/0.0307

Hc3 = ((Hc3H x 256 + Hc3L) x 5.02/65536 - 0.958)/0.0307

Err1 = Hc1 - Hr1

(convert from binary to %RH)

DS1923

Err2 = Hc2 - Hr2

Err3 = Hc3 - Hr3

2

B = [(Hr2 - Hr1 ) x (Err3 - Err1) + Hr3 x (Err1 - Err2) + Hr1 x (Err2 - Err1)]/[(Hr2 - Hr1 ) x (Hr3 - Hr1) +

(Hr3 - Hr1 ) x (Hr1 - Hr2)]

2

A = [Err2 - Err1 + B x (Hr1 - Hr2)]/(Hr2 - Hr1 )

2

C = Err1 - A x Hr1 - B x Hr1

Step 2: Execution

Hc = ((HcH x 256 + HcL) x 5.02/65536 - 0.958)/0.0307

(convert from binary to %RH)

(the actual correction)

2

Hcorr = Hc - (A x Hc + B x Hc + C)

Numerical Humidity Correction Example

CONVERTED DATA FROM CALIBRATION MEMORY

ERROR VALUES

Hr1 = 20%RH

Hr2 = 60%RH

Hr3 = 90%RH

Hc1 = 17.65%RH

Hc2 = 56.41%RH

Hc3 = 89.57%RH

Err1 = -2.35%RH

Err2 = -3.59%RH

Err3 = -0.43%RH

APPLICATION OF CORRECTION COEFFICIENTS

TO SAMPLE READING

RESULTING CORRECTION COEFFICIENTS

B = -0.186810

A = 0.001948%RH

C = 0.607143%RH

Hc = 8.9%RH

Hcorr = 9.8%RH

Note: The software correction requires floating point arithmetic (24-bit or better). Suitable math libraries for microcontrollers are

found on various websites and are included in cross-compilers.

52 ______________________________________________________________________________________

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

DS1923

Temperature compensation uses the following equation:

RH Temperature Compensation

HTcorr = (Hcorr x K + α x (T - 25°C)

The data for the software correction of humidity is taken

at 25°C. Since the temperature characteristics of the

humidity sensor are known, humidity readings taken at

other temperatures can be corrected, provided the

temperature at the time of the humidity conversion is

also known. Therefore, to obtain the most accurate

humidity results, both temperature and humidity should

be logged.

2

- β x (T - 25°C) )/(K + γ x (T - 25°C) - δ x (T - 25°C) )

Hcorr is the humidity reading with the software correc-

tion algorithm for humidity already applied, as

explained in the previous section. The function and val-

ues of the other parameters are explained in the table

below.

NAME

FUNCTION

VALUE

T

K

ꢀ

ꢁ

Temperature at the time of humidity conversion.

Humidity sensor conversion constant.

Linear compensation, enumerator.

(in °C)

0.0307

0.0035/°C

2

Quadratic compensation, enumerator.

0.000043/°C

>15°C: 0.00001/°C

ꢃ 15°C: -0.00005/°C

ꢂ

Linear compensation, denominator.

Quadratic compensation, denominator.

2

ꢄ

0.000002/°C

Numerical RH Temperature Compensation Example

SAMPLE INPUT DATA

APPLICATION OF CORRECTION COEFFICIENTS TO SAMPLE READING

ꢀ = 0.00001/°C

T = 70°C

Hcorr = 24.445%RH

2

HTcorr = (24.445 x 0.0307 + 0.0035 x 45 - 0.000043 x 45 )/(0.0307 + 0.00001 x 45 - 0.000002 x 45 )

HTcorr = 30.291%

Software Saturation Drift

Compensation

−0.3502 × k

N

∑

0.0156 × ARH × 2.54

k

HScorr = HTcorr −

1+ T − 25 /100

(

)

k=1

k

Capacitive humidity sensors read higher humidity val-

ues than the actual humidity level when they are

exposed to a high-humidity environment for an extend-

ed time period. The DS1923’s humidity sensor pro-

duces readings that are higher than the actual humidity

when exposed to humidity levels of about 70%RH and

higher. This shift continues to increase while the device

remains at 70%RH and above. This effect is called sat-

uration drift, or hysteresis. This drift is reversible.

Readings return to their regular level when the DS1923

is removed from a high-humidity environment.

ARH

The average software-corrected and tempera-

ture-compensated humidity reading of the k

hour that the device is continuously exposed

to 70%RH or higher.

k

th

T

k

The average software-corrected temperature

th

reading of the k hour that the device is

continuously exposed to 70%RH or higher.

N

The number of hours that the device is contin-

uously exposed to 70%RH or higher.

th

HTcorr The humidity reading at the end of the N

hour with the software correction algorithm for

humidity and temperature compensation

already applied. See the Software Correction

Algorithm for Humidity and RH Temperature

Compensation sections for details.

It is possible to compensate for most of the error intro-

duced by the saturation drift by post-processing tem-

perature and humidity logs using the equation below,

which is based on laboratory tests and curve-fitting

techniques.

The numbers in the equation are derived from curve fit-

ting. They apply to a time scale in hours.

______________________________________________________________________________________ 53

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

Numerical Saturation Drift Compensation Example

SAMPLE INPUT DATA (N = 8)

APPLICATION OF CORRECTION ALGORITHM

k (HOUR)

T (°C)

k

ARH (%RH)

k

PARTIAL CORRECTIONS (INDIVIDUAL ADDENDS)

1

2

3

4

5

6

7

8

25.1

91.1

92.5

92.9

93.1

93.2

93.3

93.6

93.7

1.024321

0.751140

0.544824

0.393535

0.283950

0.205086

0.148591

0.107428

25.0

DS1923

24.9

25.0

25.1

25.0

24.9

HTcorr = 93.70207%RH

Sum of partial corrections:

3.458875

HScorr = HTcorr - Sum of partial corrections

= 93.70207%RH - 3.458875%RH

HScorr = 90.24319%RH

test chamber. The drift per hour decreases the longer

the device is exposed to high humidity. The correction

algorithm compensates for the drift reasonably well. For

some applications, compensation may not be neces-

sary since the error introduced by the saturation is rela-

tively small.

The data in this example was taken from devices that

were exposed for several hours to 90%RH at 25°C in a

Pin Configuration

5.89mm

0.51mm

FRONT-SIDE BRANDING

BACK-SIDE BRANDING

16.25mm

A1

41

®

000000FBC52B

®

1-Wire

Hygrochron™

17.35mm

IO

GND

Package Information

For the latest package outline information and land patterns (footprints), go to www.maxim-ic.com/packages. Note that a “+”, “#”, or

“-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains

to the package regardless of RoHS status.

PACKAGE TYPE

PACKAGE CODE

OUTLINE NO.

21-0266

LAND PATTERN NO.

F5 iButton

IB#6HB

—

54 ______________________________________________________________________________________

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

DS1923

Revision History

REVISION REVISION

PAGES

CHANGED

DESCRIPTION

NUMBER

DATE

0

8/04

Initial release

—

Changed bullet from “Hydrophobic Filter Protects Sensor Against Dust, Dirt, Water, and

Contaminants” to “Hydrophobic Filter Protects Sensor Against Dust, Dirt, Contaminants,

and Water Droplets/Condensation”; deleted “Application Pending” from UL bullet and

safety statement; added text to the Application section: Note that the initial sealing

level of DS1923 achieves IP56. Aging and use conditions can degrade the integrity of

the seal over time, so for applications with significant exposure to liquids, sprays, or

other similar environments, it is recommended to place the Hygrochron under a shield

to protect it. (See www.maxim-ic.com/AN4126). The hydrophobic filter may not protect

the DS1923 from destruction in the event of full submersion in liquid

1

12/07

1, 4, 10

2

3

4/09

Created newer template-style data sheet

All

1

10/09

Deleted the standard part number from the Ordering Information table

Updated UL certificate reference; added “Guaranteed by design” note to Electrical

Characteristics table; deleted ꢀ from the t

specification in the Electrical

W1L

Characteristics table; applied note 13 to the t

specification in the Electrical

W0L

Characteristics table; changed RTC accuracy specification in the Electrical

Characteristics table from numbers to graph; added more details to Electrical

Characteristics table notes 4, 13, and 14; revised the last sentence of the Parasite

Power section for more clarity; added paragraph on validation certificates to Detailed

Description section; added more details on the Device Samples Counter in the Other

Indicators section

4

4/11

1–5, 11, 24

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are

implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 55

Maxim is a registered trademark of Maxim Integrated Products, Inc.


型号：	DS1923_11
厂家：	MAXIM INTEGRATED PRODUCTS
描述：	Hygrochron Temperature/Humidity Logger 温度/湿度记录仪
文件：	总55页 (文件大小：640K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

DS1923_11 [MAXIM]

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