DS1923-F5_技术文档

DS1923

Hygrochron Temperature/Humidity Logger

iButton with 8kB Data Log Memory

www.maxim-ic.com

SPECIAL FEATURES

iButton DESCRIPTION

Cꢀ Digital Hygrometer Measures Humidity with 8-Bit

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

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

(see Safe Operating Range)

The DS1923 temperature/humidity logger iButton is a

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 273hrs can be stored. In addition to

this, there are 512 bytes of SRAM for storing

application-specific information and 64 bytes for

calibration data. A mission to collect data can be

programmed to begin immediately, or after a user-

defined delay or after a temperature alarm. Access to

the memory and control functions can be password-

protected. The DS1923 is configured and

communicates with a host-computing device through

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

data lead and a ground return. Every DS1923 is

factory-lasered with a guaranteed unique 64-bit

registration number that allows for absolute

traceability. The durable stainless-steel package is

highly resistant to environmental hazards such as dirt,

moisture, and shock. Accessories permit the DS1923

to be mounted on almost any object, including

containers, pallets and bags.

Cꢀ Automatically Wakes Up, Measures Temperature

and/or Humidity and Stores Values in 8kB of

Datalog Memory in 8- or 16-Bit Format

Cꢀ Digital Thermometer Measures Temperature with

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

Cꢀ Temperature Accuracy Better than ±0.5°C from

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

Cꢀ Built-in Humidity Sensor for Simultaneous

Temperature and Humidity Logging

Cꢀ Capacitive Polymer Humidity-Sensing Element

Cꢀ Hydrophobic Filter Protects Sensor Against Dust,

Dirt, Water, and Contaminants

Cꢀ Sampling Rate from 1s up to 273hrs

Cꢀ Programmable Recording Start Delay After

Elapsed Time or Upon a Temperature Alarm Trip

Point

Cꢀ Programmable High and Low Trip Points for

Temperature and Humidity Alarms

Cꢀ Quick Access to Alarmed Devices Through

ꢀ

1-Wire Conditional Search Function

Cꢀ 512 Bytes of General-Purpose Memory Plus 64

Bytes of Calibration Memory

F5 MICROCAN

Cꢀ Two-Level Password Protection of All Memory

and Configuration Registers

5.89

0.51

Cꢀ 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

Cꢀ Individually Calibrated in a NIST-Traceable

Chamber

ꢀ

16.25

17.35

Cꢀ Calibration Coefficients for Temperature and

Humidity Factory Programmed into Nonvolatile

(NV) Memory

APPLICATIONS

Cꢀ Temperature and Humidity Logging in Food

Preparation and Processing

IO

GND

Front Side Brand

All dimensions are

Cꢀ Transportation of Temperature- and Humidity-

Sensitive Goods, Industrial Production

Cꢀ Warehouse Monitoring

shown in millimeters.

ꢀ

Cꢀ Environmental Studies/Monitoring

A1

41

ꢀ

000000FBC52B

ORDERING INFORMATION

ꢀ

1-Wire

Hygrochron^TM

PART

TEMP RANGE

PACKAGE

DS1923-F5

-20°C to +85°C F5 iButton

Back Side Brand

1-Wire and iButton are registered trademarks of Dallas Semiconductor.

Hygrochron is a trademark of Dallas Semiconductor.

1 of 52

REV: 110504

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data log Memory

DS1923 ABSOLUTE MAXIMUM RATINGS

IO Voltage to GND

-0.3V, +6V

IO Sink current

20mA

Operating Temperature and Humidity Range

-20°C to +85°C, 0%RH to 100%RH

(See Safe Operating Range Chart)

-40°C to +85°C, 0%RH to 100%RH

(See Safe Operating Range Chart)

Storage Temperature and Humidity Range

This is a stress rating only and functional operation of the device at these or any other conditions above those

indicated in the operation sections of this specification is not implied. Exposure to absolute maximum rating

conditions for extended periods of time may affect reliability.

DS1923 ELECTRICAL CHARACTERISTICS

(V_PUP= 3.0V to 5.25V, T_A= -20°C to +85°C)

PARAMETER

IO Pin General Data

1-Wire Pullup

SYMBOL

CONDITIONS

MIN

TYP

MAX UNITS

R_PUP

(Notes 1, 2)

(Note 3)

2.2

kꢀ

Resistance

Input Capacitance

Input Load Current

High-to-Low Switching

Threshold

C_IO

I_L

100

6

800

10

pF

µA

IO pin at V_PUP

(Notes 4. 5)

(Notes 1, 6)

(Notes 4, 7)

V_TL

V_IL

0.4

3.2

0.3

3.4

V

Input Low Voltage

Low-to-High Switching

Threshold

V_TH

0.7

Switching Hysteresis

Output Low Voltage

V_HY

V_OL

(Note 8)

0.09

N/A

0.4

V

At 4mA (Note 9)

5

2

Standard speed, R_PUP= 2.2kꢀ

Overdrive speed, R_PUP= 2.2kꢀ

Overdrive speed, directly prior to

reset pulse; R_PUP= 2.2kꢀ

Recovery Time

(Note 1)

t_REC

µs

5

Rising-Edge Hold-off

Time

t_REH

(Note 10)

0.6

2.0

µs

Standard speed

65

8

Timeslot Duration

(Note 1)

t_SLOT

Overdrive speed, V_PUP> 4.5V

Overdrive speed (Note 11)

9.5

IO Pin, 1-Wire Reset, Presence Detect Cycle

Standard speed, V_PUP> 4.5V

480

690

48

720

80

60

63.5

7

Reset Low Time

(Note 1)

Standard speed (Note 11)

Overdrive speed, V_PUP> 4.5V

Overdrive speed (Note 11)

Standard speed, V_PUP> 4.5V

Standard speed (Note 11)

Overdrive speed (Note 11)

Standard speed, V_PUP> 4.5V

Standard speed

t_RSTL

µs

70

15

Presence-Detect High

Time

t_PDH

µs

15

2

1.5

0.15

60

5

Presence-Detect Fall

Time

t_FPD

8

(Note 12)

Overdrive speed

1

Standard speed, V_PUP> 4.5V

Standard speed (Note 11)

Overdrive speed, V_PUP> 4.5V

(Note 11)

240

287

60

Presence-Detect Low

Time

t_PDL

µs

7

24

Overdrive speed (Note 11)

Standard speed, V_PUP> 4.5V

Standard speed

7

65

71.5

8

28

75

9

Presence-Detect

Sample Time

(Note 1)

t_MSP

Overdrive speed

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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

MAX UNITS

IO Pin, 1-Wire Write

Standard speed

60

6

120

Write-0 Low Time

(Note 1)

Overdrive speed, V_PUP> 4.5V

(Note 11)

t_W0L

µs

12

Overdrive speed (Note 11)

Standard speed

Overdrive speed

7.5

5

1

12

15 - ꢁ

1.95 - ꢁ

Write-1 Low Time

(Notes 1, 13)

t_W1L

IO Pin, 1-Wire Read

Read Low Time

(Notes 1, 14)

5

Standard speed

Overdrive speed

Standard speed

Overdrive speed

15 - ꢂ

1.95 - ꢂ

15

t_RL

µs

1

Read Sample Time

t_RL+ ꢂ

t_MSR

(Notes 1, 14)

1.95

Real-Time Clock

min./

month

PPM

Accuracy

+25°C

-3

+3

Frequency Deviation

Temperature Converter

Conversion Time

-300

+60

-20°C to +85°C

ꢃ

F

8-bit mode (Note 15)

16-bit mode (11 bits)

30

75

t_CONV

ms

s

240

600

Thermal Response

Time Constant

iButton package (Note 16)

(Notes 15, 17, 18, 19)

130

ꢄ

RESP

Conversion Error

Without Software

Correction

See Temperature

Accuracy Graphs

°C

ꢃꢅ

Conversion Error With

Software Correction

See Temperature

Accuracy Graphs

Humidity Converter (Note 30)

ꢄ

Humidity Response

Slow moving air (Note 20)

(Note 21)

30

s

RH

Time Constant

8

12

bits

RH Resolution

0.64

0

0.04

100

%RH

RH Range

(Note 22)

RH Accuracy and

Interchangeability

RH Nonlinearity

RH Hysteresis

With software correction

(Notes 18, 19, 23, 24, 25)

With software correction (Note 18)

(Notes 26, 27)

±5

%RH

<1

0.5

%RH

RH Repeatability

Long-Term Stability

(Note 28)

±0.5

<1.0

At 50%RH (Note 29)

%RH/y

Note 1:

Note 2:

System requirement.

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 found in the DS2480B may be required.

Note 3:

Capacitance on the data pin could be 800pF when V_PUPis first applied. If a 2.2kꢀ resistor is used to pull up the data line 2.5µs

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

V_TL, V_THare a function of the internal supply voltage.

Note 4:

Note 5:

Note 6:

Note 7:

Note 8:

Note 9:

Note 10:

Note 11:

Note 12:

Voltage below which, during a falling edge on IO, a logic '0' is detected.

The voltage on IO needs to be less or equal to V_ILMAXwhenever the master drives the line low.

Voltage above which, during a rising edge on IO, a logic '1' is detected.

After V_THis crossed during a rising edge on IO, the voltage on IO has to drop by V_HYto be detected as logic '0'.

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

The earliest recognition of a negative edge is possible at t_REHafter V_THhas been previously reached.

Highlighted numbers are NOT in compliance with the published iButton standards. See comparison table below.

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_PUPand the time at which the voltage is 10% of V_PUP

.

Note 13:

Note 14:

ꢁ represents the time required for the pullup circuitry to pull the voltage on IO up from V_ILto V_TH

.

ꢂ represents the time required for the pullup circuitry to pull the voltage on IO up from V_ILto the input high threshold of the bus

master.

Note 15:

Note 16:

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

This number was derived from a test conducted by Cemagref in Antony, France, in July of 2000.

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

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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

Note 17:

Note 18:

Note 19:

For software corrected accuracy, assume correction using calibration coefficients with calibration equations for error

compensation.

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

at: http://www.ibutton.com.

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, 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 recommended when supplemental or redundant

information sources are used. Data logger products are 100% tested and calibrated at time of manufacture by Dallas

Semiconductor/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 temperature accuracy of the product to ensure it is still operating properly.

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

is slower. Test was performed at 5L/min airflow.

Note 20:

Note 21:

Note 22:

Note 23:

All DS1923 humidity measurements are 12-bit readings. Missioning determines 8-bit or 16-bit data logging. Battery lifetime is the

same no matter what RH resolution is logged.

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.

Software corrected accuracy is accomplished using the method detailed in the Software Correction Algorithm for Temperature

section of this data sheet.

Note 24:

Note 25:

Note 26:

Every DS1923 Device is measured and calibrated in a controlled, NIST-traceable RH environment.

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

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

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

continuous 80%RH for 30 minutes.

Note 27:

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 of this data sheet.

Note 28:

Note 29:

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

samples as is reasonable.

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 Safe Operating Range chart). For maximum long-term stability, the sensor should not be

exposed or subjected to organic solvents, corrosive agents (strong acids, SO₂, H₂SO₄, CI₂,HCL, H₂S, etc.) and strong bases

(compounds with PH greater than 7). Dust settling on the filter surface does not affect the sensor performance except to possibly

decrease the speed of response.

For more information on the RH sensor’s tolerance to chemicals visit:

http://content.honeywell.com/sensing/prodinfo/humiditymoisture/technical/c15_144.pdf

Note 30:

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

Standard Values

DS1923 Values

Standard Speed

Parameter

Standard Speed

Overdrive Speed

Name

t_SLOT(incl. t_REC

t_RSTL

Min

Max

(undef.)

60µs

Min

Max

(undef.)

80µs

Min

65µs¹⁾

690µs

15µs

Max

(undef.)

720µs

63.5µs

287µs

120µs

Min

Max

(undef.)

80µs

)

61µs

7µs

9.5µs

480µs

15µs

60µs

48µs

2µs

8µs

6µs

70µs

2µs

t_PDH

6µs

7µs

t_PDL

240µs

24µs

60µs

7µs

28µs

t_W0L

120µs

16µs

60µs

7.5µs

12µs

¹⁾Intentional change, longer recovery time requirement due to modified 1-Wire front end.

PHYSICAL SPECIFICATION

Weight

Safety

Size

See mechanical drawing

Ca. 5.0 grams

Meets UL#913 (4^thEdit.); Intrinsically Safe Apparatus,

approval under Entity Concept for use in Class I,

Division 1, Group A, B, C, and D Locations (application

pending)

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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

Safe Operating Range

100

80

60

40

20

0

Safe Operating Zone

-40

-20

0

20

40

60

80

Temperature (°C)

DS1923 Temperature Accuracy

Uncorrected Max Error

SW Corrected Max Error

Uncorrected Min Error

SW Corrected Min Error

2.0

1.5

1.0

0.5

0.0

-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.

5 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

Minimum Lifetime vs. Temperature, Slow Sampling Temperature Only

Every Minute

Every 60 Min.

Every 3 Min.

No Samples

Every 10 Min.

Osc. Off

10

9

8

7

6

5

4

3

2

1

0

-20

-10

0

10

20

30

40

50

60

70

80

DS1923: Temperature (°C)

Every Minute

Every 30 Min.

No Samples

Every 3 Min.

Every 60 Min.

Osc. Off

Every 10 Min.

Every 300 Min.

10

9

8

7

6

5

4

3

2

1

0

-20

-10

0

10

20

30

40

50

60

70

80

DS1923: Temperature (°C)

6 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

Minimum Lifetime vs. Temperature, Fast Sampling Temperature Only

Every Second

Every 30 Sec.

Every 3 Sec.

Every 60 Sec.

Every 10 Sec.

350

300

250

200

150

100

50

0

-20

-10

0

10

20

30

40

50

60

70

80

DS1923: Temperature (°C)

Every Second

Every 30 Sec.

Every 3 Sec.

Every 60 Sec.

Every 10 Sec.

100

80

60

40

20

0

-20

-10

0

10

20

30

40

50

60

70

80

DS1923: Temperature (°C)

7 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

Minimum Lifetime vs. Temperature, Slow Sampling, Temperature with Humidity

Every Minute

Every 60 Min.

Every 3 Min.

No Samples

Every 10 Min.

Osc. Off

10

9

8

7

6

5

4

3

2

1

0

-20

-10

0

10

20

30

40

50

60

70

80

DS1923: Temperature (°C)

Minimum Lifetime vs. Temperature, Fast Sampling, Temperature with Humidity

Every Second

Every 30 Sec.

Every 3 Sec.

Every 60 Sec.

Every 10 Sec.

350

300

250

200

150

100

50

0

-20

-10

0

10

20

30

40

50

60

70

80

DS1923: Temperature (°C)

8 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

Minimum Product Lifetime vs. Sample Rate (Temperature Only)

0°C

40°C

60°C

75°C

85°C

10

1

0.1

0.01

0.1

1

10

100

DS1923: Minutes between Samples

NOTE: With humidity logging activated, the lifetime is reduced by less than 11% for sample rate of 3 minutes and

slower and by a maximum of 20% for sample rate of 1 minute and faster.

0°C

40°C

60°C

75°C

85°C

10

1

0.1

0.01

0.001

0.01

0.1

1

10

100

DS1923: 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.

9 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

COMMON iButton FEATURES

Cꢀ Digital Identification and Information by Momentary Contact

Cꢀ Unique Factory-Lasered 64-Bit Registration Number Assures Error-Free Device Selection and Absolute

Traceability Because No Two Parts are Alike

Cꢀ Built-in Multidrop Controller for 1-Wire Net

Cꢀ Chip-Based Data Carrier Compactly Stores Information

Cꢀ Data can be Accessed While Affixed to Object

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

Cꢀ Durable Stainless-Steel Case Engraved with Registration Number Withstands Harsh Environments

Cꢀ Easily Affixed with Self-Stick Adhesive Backing, Latched by its Flange, or Locked with a Ring Pressed onto its

Rim

Cꢀ Presence Detector Acknowledges when Reader First Applies Voltage

Cꢀ Meets UL#913 (4th Edit.); Intrinsically Safe Apparatus: Approved Under Entity Concept for use in Class I,

Division 1, Group A, B, C, and D Locations (Application Pending)

EXAMPLES OF ACCESSORIES

DS9096P

DS9101

Self-Stick Adhesive Pad

Multipurpose Clip

Mounting Lock Ring

Snap-In Fob

DS9093RA

DS9093A

DS9092

iButton Probe

APPLICATION

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 climatic 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. Software for setup and data

retrieval through the 1-Wire interface is available for free download from the iButton website (www.ibutton.com).

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- or equipment-specific data files.

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: 1) 64-bit lasered ROM, 2) 256-bit scratchpad, 3) 512-byte

general-purpose SRAM, 4) two 256-bit register pages of timekeeping, control, status, and counter registers and

passwords, 5) 64 bytes of calibration memory, and 6) 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 memory, counter

registers and several other registers are read-only for the user. Both register pages are write-protected while the

device is programmed for a mission. The password registers, one for a read password and another one for a

read/write password can only be written to but never read.

The hierarchical structure of the 1-Wire protocol is shown in Figure 2. The bus master must first provide one of the

eight ROM function commands: 1) Read ROM, 2) Match ROM, 3) Search ROM, 4) Conditional Search ROM, 5)

Skip ROM, 6) Overdrive-Skip ROM, 7) Overdrive-Match ROM, or 8) Resume. Upon completion of an Overdrive

ROM command byte 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 executed, the memory and control functions become

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 significant bit first.

10 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

Figure 1. DS1923 BLOCK DIAGRAM

ROM

64-Bit

Lasered

ROM

Parasite

Powered

Circuitry

1-Wire

Port

Function

Control

IO

Memory

256-Bit

Scratchpad

Function

Control

3V Lithium

General-Purpose

SRAM

(512 Bytes)

Internal

DS1923

32.768 kHz

Oscillator

Register Pages

(64 Bytes)

Timekeeping &

Control Reg. &

Counters

Calibration Memory

(64 Bytes)

Thermal

Sense

ADC1

Datalog

Memory

8K Bytes

Humidity

Sensor and

ADC2

Control

Logic

PARASITE POWER

The block diagram (Figure 1) shows the parasite-powered 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 conserved, and 2) if the

battery is exhausted for any reason, the ROM may still be read.

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 CRC of the first 56 bits. See Figure 4 for details. The 1-

Wire CRC is generated using a polynomial generator consisting of a shift register and XOR gates as shown in

Figure 3. The polynomial is X⁸+ X⁵+ X⁴+ 1. Additional information about the Dallas 1-Wire Cyclic Redundancy

Check is available in Dallas Application Note 27.

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, then the serial number followed by the

temperature range code is entered. After the range code has been entered, the shift register contains the CRC

value. Shifting in the 8 bits of CRC returns the shift register to all 0s.

11 of 52

Figure 2. HIERARC^DH^SI¹C⁹²A^3:L^HS^ygT^roR^chU^roC^{n T}T^eU^mR^peE^ratuF^rO^e/HR^um1^id-W^{ity L}ir^oe^ggP^erR^iBO^uttT^onO^wC^ithO⁸L^{kB Data Log Memory}

1-Wire net

Other

BUS

Devices

Master

DS1923

Command

Level:

Available

Data Field

Affected:

Commands:

Read ROM

64-bit ROM, RC-Flag

64-bit ROM, RC-Flag, Alarm Flags,

Search Conditions

Match ROM

Search ROM

1-Wire ROM Function

Conditional Search ROM

Commands

Skip ROM

RC-Flag

Resume

RC-Flag

Overdrive Skip

Overdrive Match

RC-Flag, OD-Flag

64-bit ROM, RC-Flag, OD-Flag

Write Scratchpad

256-bit Scratchpad, Flags

256-bit Scratchpad

Read Scratchpad

Copy Scratchpad w/PW

512 byte Data Memory, Registers,

Flags, Passwords

Read Memory w/PW &

w/CRC

Memory, Registers, Passwords

DS1923-specific

Memory Function

Commands

Clear Memory w/PW

Mission Time Stamp, Mission Samples

Counter, Start Delay, Alarm

Flags, Passwords

Forced Conversion

Start Mission w/PW

Memory addresses 020C to 020Fh

Flags, Timestamp, Memory addresses

020C to 020Fh (when logging)

Flags

Stop Mission w/PW

Figure 3. 1-Wire CRC GENERATOR

Polynomial = X⁸+ X⁵+ X⁴+ 1

1^st

2^nd

3^rd

4^th

5^th

6^th

7^th

8^th

STAGE STAGE

X¹

STAGE STAGE

X³

STAGE

STAGE STAGE STAGE

X⁰

X²

X⁴

X⁵

X⁶X⁷

INPUT DATA

X⁸

12 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

Figure 4. 64-BIT LASERED ROM

MSB

LSB

8-Bit

CRC Code

8-Bit Family

48-Bit Serial Number

Code (41h)

LSB MSB LSB

MSB LSB

MSB

MEMORY

The memory map of the DS1923 is shown in Figure 5. The 512 bytes general-purpose SRAM are located in pages

0 through 15. The various registers to set up and control the device fill page 16 and 17, called Register Pages 1

and 2 (details in Figure 6). Pages 18 and 19 provide storage space for calibration data. The "data log" logging

memory starts at address 1000h (page 128) and extends over 256 pages. The memory pages 20 to 127 are

reserved for future extensions. The scratchpad is an additional page that acts as a buffer when writing to the

SRAM memory or the register page. The data memory can be written at any time. 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 recommended. See the Security by Password section for ways to

protect the memory. The access type for the register pages is register-specific and depends on 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 supervision of the on-chip control logic. Due to the special 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 and the calibration memory. See the Address Register and Transfer Status section for details.

Figure 5. DS1923 MEMORY MAP

32-Byte Intermediate Storage Scratchpad

ADDRESS

0000H to

32-Byte General-Purpose SRAM (R/W)

General-Purpose SRAM (R/W)

Page 0

001FH

Pages 1

to 15

0020H to

01FFH

0200H to

021FH

0220H to

023FH

0240H to

025FH

0260H to

027FH

0280H to

0FFFH

1000H to

2FFFH

32-Byte Register Page 1

32-Byte Register Page 2

Page 16

Page 17

Calibration Memory Page 1 (R/W)

Calibration Memory Page 2 (R/W)

(Reserved For Future Extensions)

Page 18

Page 19

Pages 20 to 127

Pages 128

to 383

Data Log Memory (Read-Only)

13 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

Figure 6. DS1923 REGISTER PAGES MAP

ADDR

0200h

0201h

b7

0

b6

b5

b4

b3

b2

b1

b0

Function

Access*

10 Seconds

10 Minutes

Single Seconds

Single Minutes

0

Real-

Time

20h.

0202h

0

12/24

10h.

Single Hours

R/W; R

AM/PM

Clock

0203h

0204h

0205h

0206h

0207h

0208h

0209h

020Ah

020Bh

020Ch

020Dh

020Eh

020Fh

0210h

0211h

0212h

0213h

0214h

0215h

0216h

0217h

0218h

0219h

021Ah

0

10 Date

Single Date

Single Months

Single Years

Registers

CENT

0

10m.

10 Years

Low Byte

Sample

Rate

R/W; R

0

High Byte

Low Threshold

High Threshold

Low Threshold

High Threshold

Temp.

Alarms

Humidity

Alarms

Latest

R/W; R

R; R

Low Byte

0

High Byte

Temp.

Low Byte

High Byte

Latest

R; R

Humidity

T.Alm.En.

0

1

0

1

0

1

0

1

0

1

ETHA

EHHA

EHSS

EHL

ETLA

R/W; R

R; R

1

0

EHLA H.Alm.En.

0

EOSC

ETL

TLF

0

RTC En.

Mis. Cntrl.

Alm. Stat.

Gen. Stat.

Start

1

SUTA

RO

1

HLFS

HHF

MEMCLR

TLFS

HLF

0

BOR

1

0

THF

WFTA

MIP

R; R

Low Byte

Center Byte

High Byte

Delay

R/W; R

Counter

0

10 Seconds

10 Minutes

Single Seconds

Single Minutes

Mission

Time

20h.

021Bh

021Ch

0

12/24

10h.

Single Hours

R; R

AM/PM

0

10 Date

Single Date

Single Months

Single Years

Stamp

021Dh CENT

021Eh

021Fh

0220h

0221h

0222h

0223h

0224h

0225h

0226h

0227h

0228h

Z

0

10m.

10 Years

(No Function; Reads 00h)

Low Byte

(N/A)

Mission

Sample

Counter

Device

Sample

Counter

Flavor

R; R

Center Byte

High Byte

Low Byte

Center Byte

High Byte

Configuration Code

EPW

R; R

PW. Cntrl.

Read

R/W; R

First Byte

Access

Password

Full

Z

W; Z

R; R

022Fh

0230h

Z

Eighth Byte

First Byte

Z

Access

Password

0237h

0238h

Z

Eighth Byte

(No Function; All of These Bytes Read 00h)

(N/A)

023Fh

Note: The first entry in column ACCESS TYPE is valid between missions. The second entry shows the applicable

access type while a mission is in progress.

14 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

TIMEKEEPING AND CALENDAR

The real-time clock/alarm and calendar information is accessed by reading/writing the appropriate bytes in the

register page, address 200h to 205h. For readings to be valid, all RTC registers must be read sequentially starting

at address 0200h. Some of the RTC bits are set to 0. These bits always read 0 regardless of how they are written.

The number representation of the real-time clock registers is BCD format (Binary-Coded Decimal).

Real-Time Clock and RTC Alarm Register Bitmap

ADDR

0200h

0201h

0202h

b7

0

b6

b5

b4

b3

b2

b1

b0

10 Seconds

10 Minutes

Single Seconds

Single Minutes

0

20h.

0

12/24

10h.

Single Hours

AM/PM

0203h

0204h

0205h

0

10 Date

Single Date

Single Months

Single Years

CENT

0

10m.

10 Years

The real-time clock of the DS1923 can run in either 12-hour or 24-hour mode. Bit 6 of the Hours Register (address

202h) is defined as the 12- or 24-hour mode select bit. When high, the 12-hour mode is selected. In the 12-hour

mode, bit 5 is the AM/PM bit with logic 1 being PM. In the 24-hour mode, bit 5 is the 20-hour bit (20 to 23 hours).

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.

The calendar logic is designed to automatically compensate for leap years. For every year value that is either 00 or

a multiple of 4 the device will add a 29th of February. This will work correctly up to (but not including) the year

2100.

SAMPLE RATE

The content of the Sample Rate Register (addresses 0206h, 0207h) specifies the time elapse (in seconds if EHSS

= 1, or minutes if EHSS = 0) between two temperature/humidity logging events. The sample rate can be any value

from 1 to 16383, coded as an unsigned 14-bit binary number. If EHSS = 1, the shortest time between logging

events is 1 second and the longest (sample rate = 3FFFh) is 4.55 hours. If EHSS = 0, the shortest is 1 minute and

the longest time is 273.05 hours (sample rate = 3FFFh). The EHSS bit is located in the RTC Control Register at

address 0212h. It is important that the user sets the EHSS bit accordingly while setting the Sample Rate register. A

sample rate of 0000h is not valid and must be avoided under all circumstances. This causes the device to

enter into an unrecoverable state.

Sample Rate Register Bitmap

ADDR

0206h

0207h

b7

b6

b5

b4

Sample Rate Low

Sample Rate High

b3

b2

b1

b0

0

During a mission, there is only read access to these registers. Bits cells marked "0" always read 0 and cannot be

written to 1.

TEMPERATURE CONVERSION

The DS1923 measures temperatures in the range of -20°C to +85°C. Temperature values are represented as a 8-

or 16-bit unsigned binary number with a resolution of 0.5°C in the 8-bit mode and 0.0625°C in the 16-bit mode.

The higher temperature byte TRH is always valid. In the 16-bit mode only the three highest bits of the lower byte

TRL are valid. The five lower bits all read zero. 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.

15 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

Latest Temperature Conversion Result Register Bitmap

ADDR

020Ch

020Dh

b7

b6

T1

T9

b5

T0

T8

b4

b3

b2

b1

0

b0

0

T2

0

TRL

TRH

T10

T7

T6

T5

T4

T3

With TRH and TRL representing the decimal equivalent of a temperature reading the temperature value is

calculated as

ꢀ(°C) = TRH/2 - 41 + TRL/512

ꢀ(°C) = TRH/2 - 41

(16-bit mode, TLFS = 1, see address 0213h)

(8-bit mode, TLFS = 0, see address 0213h)

This equation is valid for converting temperature readings 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 equation above needs to be resolved to

TALM = 2 * ꢀ (°C) + 82

Since the temperature alarm threshold is only one byte, the resolution or temperature increment is limited to 0.5°C.

The TALM value needs to be converted into hexadecimal 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- or 16-bit) only the most significant byte of a temperature conversion is used to determine

whether an alarm is generated.

Temperature Conversion Examples

TRH

TRL

Mode

ꢀ(°C)

hex

decimal hex

decimal

8-bit

54h

84

23

84

23

1.0

Z

0

8-bit

17h

54h

17h

-29.5

1.000

Z

16-bit

00h

60h

96

-29.3125

Temperature Alarm Threshold Examples

TALM

ꢀ(°C)

hex

85h

3Eh

decimal

133

25.5

-10.0

62

HUMIDITY CONVERSION

In addition to temperature, the DS1923 can log humidity data in 8-bit or 16-bit format. Humidity values are

represented as 8- 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.

The DS1923 reads data from its humidity sensor whenever a Forced Conversion command is executed (see

Memory/Control Function Commands) or during a mission, if the device is set up to log humidity 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 will 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.

16 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

Latest Humidity Conversion Result Register Bitmap

ADDR

020Eh

020Fh

b7

b6

b5

H1

H9

b4

H0

H8

b3

b2

b1

X

b0

X

H3

H2

X

HRL

HRH

H11

H10

H7

H6

H5

H4

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 * 256 + HRL)/16

Round IVAL down to the nearest integer; this eli-

minates the undefined 4 bits of HRL.

ADVAL = IVAL*5.02/4096

ADVAL = HRH*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.

To specify the humidity alarm thresholds, the equation needs to be resolved to:

ADVAL = HUMIDITY(%RH) * 0.0307 + 0.958

HALM = ADVAL * 256/5.02

Round HALM to the nearest integer.

The HALM value needs to be converted into hexadecimal before it can be written to one of the humidity alarm

threshold registers (Low Alarm address 020Ah; High Alarm address 020B). Independent of the conversion

mode (8-or 16-bit) only the most significant byte of a humidity conversion is used to determine whether an alarm

will be generated. The alarm thresholds are applied to the raw humidity readings. Therefore, if software correction

is used, the effect of the software correction is to be reversed before calculating a humidity alarm threshold.

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.

Humidity Conversion Examples

HRH

HRL

Mode

Humidity(%RH)

hex

decimal hex

decimal

8-bit

B5h

181

103

181

103

84.41

34.59

84.89

34.70

Z

12

48

8-bit

67h

B5h

67h

Z

16-bit

C0h

30h

Humidity Alarm Threshold Examples

HALM

Humidity(%RH)

hex

97h

58h

decimal

151

65

25

88

These examples do not include the effects of software correction.

17 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

TEMPERATURE SENSOR ALARM

The DS1923 has two Temperature Alarm Threshold registers (address 0208h, 0209h) to store values, which

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.

Temperature Sensor Control Register Bitmap

ADDR

b7

b6

b5

b4

b3

b2

0

b1

b0

0210h

0

ETHA

ETLA

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.

Register Details

Bit Description

Bit(s)

Definition

This bit controls whether, during a mission, the Temperature Low Alarm

Flag TLF can be set, if a temperature conversion 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.

ETLA: Enable Tempera-

ture Low Alarm

b0

This bit controls whether, during a mission, the Temperature High Alarm

Flag THF can be set, if a temperature conversion 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.

ETHA: Enable

b1

Temperature High Alarm

HUMIDITY ALARM

The DS1923 has two Humidity Alarm Threshold registers (address 020Ah, 020Bh) to store values, which

determine 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 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.

Humidity Sensor Control Register Bitmap

ADDR

b7

b6

b5

b4

b3

1

b2

1

b1

b0

0211h

1

EHHA

EHLA

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.

Register Details

Bit Description

Bit(s)

Definition

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.

EHLA: Enable Humidity

Low Alarm

b0

This bit controls whether, during a mission, the Humidity High Alarm

Flag HHF can be set, if a value from the humidity 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, humidity

high alarms are not generated.

EHHA: Enable Humidity

High Alarm

b1

18 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

REAL-TIME CLOCK CONTROL

To minimize the power consumption of a DS1923, the real-time clock oscillator should be turned off when 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 specified in seconds or minutes.

RTC Control Register Bitmap

ADDR

b7

b6

b5

b4

0

b3

0

b2

0

b1

b0

0212h

0

EHSS

EOSC

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.

Register Details

Bit Description

Bit(s)

Definition

This bit controls the crystal oscillator of the real-time clock. When set to

logic 1, the oscillator starts operation. 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 temperature or humidity

conversion must not be attempted while the RTC oscillator is

stopped. This causes the device to enter into an unrecoverable state.

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.

EOSC: Enable Oscillator

b0

EHSS: Enable High Speed

Sample

b1

MISSION CONTROL

The DS1923 is set up for its operation by writing appropriate 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) is to be used and whether old data can be overwritten by new data,

once the data log memory is full. An additional control bit can be set to tell the DS1923 to wait with logging data

until a temperature alarm is encountered.

Mission Control Register Bitmap

ADDR

b7

b6

b5

b4

b3

b2

b1

b0

0213h

1

SUTA

RO

HLFS

TLFS

EHL

ETL

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.

Register Details

Bit Description

Bit(s)

Definition

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.

ETL: Enable Temperature

Logging

b0

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 will 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 temperature, typically both, humidity and temperature

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

EHL: Enable Humidity

Logging

b1

b2

This bit specifies the format used to store temperature readings in the

data log memory. If this bit is 0, the data will be stored in 8-bit format. If

this bit is 1, the 16-bit format will be used (higher resolution). With 16-bit

format, the most-significant byte is stored at the lower address.

TLFS: Temperature

Logging Format Selection

19 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

Bit Description

Bit(s)

Definition

This bit specifies the format used to store humidity readings in the data

log memory. If this bit is 0, the data will be 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.

HLFS: Humidity Logging

Format Selection

b3

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 beginning, overwriting previously collected data.

If this bit is 0, the logging and conversions will stop once the data log

memory is full. However, the RTC will continue to run and the MIP bit

will remain set until the Stop Mission command is performed.

This bit specifies whether a mission begins immediately (includes

delayed start) or if a temperature alarm will be required to start the

mission. If this bit is 1, the device will perform a temperature conversion

at the selected sample rate and begin with data logging only if an

alarming temperature (high alarm or low alarm) was found. The first

logged temperature will be when the alarm occurred. However, the

Mission Sample Counter will not increment. The Start Upon Tempera-

ture Alarm function is only available if temperature logging is enabled

(ETL = 1).

RO: Rollover Control

b4

b5

SUTA: Start Mission upon

Temperature Alarm

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

command (see ROM Function Commands). The humidity and temperature alarm only occurs if enabled (see

Temperature Sensor Alarm and Humidity Alarm). The BOR alarm is always enabled.

Alarm Status Register Bitmap

ADDR

b7

b6

b5

b4

1

b3

b2

b1

b0

0214h

BOR

1

HHF

HLF

THF

TLF

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 function is invoked. See Memory and Control Functions for

details.

Register Details

Bit Description

Bit(s)

Definition

If this bit reads 1, there was at least one temperature conversion during

a mission revealing a temperature equal to or lower than the value in the

Temperature Low Alarm Register. A forced conversion can affect the

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

mode.

TLF: Temperature Low

Alarm Flag

b0

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.

THF: Temperature High

Alarm Flag

b1

If this bit reads 1, there was at least one humidity reading during a

mission revealing a value equal to or lower than the value in the Humi-

dity Low Alarm Register. A forced conversion can affect the HLF bit.

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 Humi-

dity High Alarm Register. A forced conversion can affect the HHF bit.

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.

HLF: Humidity Low Alarm

Flag

b2

b3

HHF: Humidity High Alarm

Flag

BOR: Battery On Reset

Alarm

b7

20 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

GENERAL STATUS

The information in the general status register tells the host computer whether a mission-related command was

executed successfully. Individual status bits indicate whether the DS1923 is performing a mission, waiting for a

temperature alarm to trigger the logging of data or whether the data from the latest mission has been cleared.

General Status Register Bitmap

ADDR

b7

b6

b5

b4

b3

b2

0

b1

b0

0

MEMCLR

0215h

1

0

WFTA

MIP

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

Register Details

Bit Description

Bit(s)

Definition

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 function commands Start Mission and

Stop Mission.

MIP: Mission In Progress

b1

If this bit reads 1, the Mission Time Stamp, Mission Sample Counter, as

well as 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 sections. The MEMCLR bit returns to 0

as soon as a new mission is started by using the Start Mission

command. The memory has to be cleared in order for a mission to start.

If this bit reads 1, the Mission Start upon Temperature Alarm was

selected and the Start Mission command was successfully executed, but

the device has not yet experienced 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.

MEMCLR: Memory

Cleared

b3

b4

WFTA: Waiting for

Temperature Alarm

MISSION START DELAY

The content of the Mission Start Delay Counter tells how many minutes have to expire from the time a mission was

started until the first measurement of the mission will take place (SUTA = 0) or until the device will start testing the

temperature for a temperature alarm (SUTA = 1). The Mission Start Delay is stored as an unsigned 24-bit integer

number. The maximum delay is 16777215 minutes, equivalent to 11650 days or roughly 31 years. If the start delay

is non-zero and the SUTA bit is set to 1, first the delay has to expire before the device starts testing for temperature

alarms to begin logging data.

Mission Start Delay Counter

ADDR

0216h

0217h

0218h

b7

b6

b5

b4

b3

b2

b1

b0

Delay Low Byte

Delay Center Byte

Delay High Byte

During a mission, there is only read access to these registers.

For a typical mission, the Mission Start Delay is 0. If a mission is too long for a single DS1923 to store all readings

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.

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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

MISSION TIME STAMP

The Mission Time Stamp indicates the date and time of the first temperature and/or humidity sample of the

mission. There is only read access to the Mission Time Stamp Register.

Mission Time Stamp Registers Bitmap

ADDR

0219h

021Ah

021Bh

b7

b6

b5

b4

b3

b2

b1

b0

0

10 Seconds

Single Seconds

Single Minutes

Single Hours

0

10 Minutes

20h.

0

12/24

10h.

10m.

AM/PM

021Ch

0

10 Date

Single Date

021Dh CENT

0

Single Months

021Eh

10 Years

Single Years

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 Sample Counter together with the starting address and the logging format (8 or

16 bits) provides the information to identify valid blocks of data that have been gathered during the current (MIP =

1) or latest mission (MIP = 0). See section Data log Memory Usage for an illustration. Note that when SUTA = 1,

the Mission Sample Counter does not increment when the first sample is logged.

Mission Sample Counter Register Map

ADDR

0220h

0221h

0222h

b7

b6

b5

b4

b3

b2

b1

b0

Low Byte

Center Byte

High Byte

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 Sample Counter and Device Sample

Counter.

The number read from the Mission Sample Counter indicates how often the DS1923 woke up during a mission to

measure temperature and/or humidity. The number format is 24-bit unsigned integer. The Mission Sample Counter

is reset through the Clear Memory command.

OTHER INDICATORS

The Device Sample Counter is similar to the Mission Sample Counter. 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

SUTA mode. Between missions the counter increments whenever the Forced Conversion command is executed.

This way the Device Sample Counter functions like a gas gauge for the battery that powers the iButton.

Device Sample Counter Register Map

ADDR

0223h

0224h

0225h

b7

b6

b5

b4

b3

b2

b1

b0

Low Byte

Center Byte

High Byte

There is only read access to this register.

The Device Sample Counter is reset to zero when the iButton is assembled. The counter increments a couple of

times during final test. The number format is 24-bit unsigned integer. The maximum number that can be

represented in this format is 16777215.

The Device Configuration Byte is used to allow the master to distinguish between the DS2422 chip, and the

DS1923, DS1922L, and DS1922T iButtons. The table below shows the codes assigned to the various devices.

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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

Device Configuration Byte

ADDR

0226h

b7

b6

b5

b4

b3

0

b2

0

b1

0

b0

0

DS2422

DS1923

DS1922L

DS1922T

0

1

0

1

0

1

0

There is only read access to this register.

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 needs to

be transmitted right after the command code of the memory or control function. If password checking is enabled the

password transmitted is compared to the passwords stored in the device. The data pattern stored in the Password

Control register determines whether password checking is enabled.

Password Control Register

ADDR

b7

b6

b5

b4

b3

b2

b1

b0

0227h

EPW

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

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 will be 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.

Before enabling password checking, passwords for read-only access as well as for full access (read/write/control)

need to be written to the password registers. Setting up a password or enabling/disabling 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 redefined at the same time.

Read Access Password Register

ADDR

0228h

0229h

Z

b7

b6

b5

b4

b3

b2

b1

b0

RP0

RP8

Z

RP7

RP15

RP6

RP14

RP5

RP13

RP4

RP12

Z

RP3

RP11

RP2

RP10

RP1

RP9

022Eh

022Fh

RP55

RP63

RP54

RP62

RP53

RP61

RP52

RP60

RP51

RP59

RP50

RP58

RP49

RP57

RP48

RP56

There is only write access to this register. Attempting to read the password will report all zeros. The password

cannot be changed while a mission is in progress.

The Read Access Password needs to be transmitted exactly in the sequence RP0, RP1… RP62, RP63. This

password only applies to the function “Read Memory with CRC”. The DS1923 delivers the requested data only if

the password transmitted by the master was correct or if password checking is not enabled.

Full-Access Password Register

ADDR

0230h

0231h

Z

b7

b6

b5

b4

b3

b2

b1

b0

FP0

FP8

Z

FP7

FP15

FP6

FP14

FP5

FP13

FP4

FP12

Z

FP3

FP11

FP2

FP10

FP1

FP9

0236h

0237h

FP55

FP63

FP54

FP62

FP53

FP61

FP52

FP60

FP51

FP59

FP50

FP58

FP49

FP57

FP48

FP56

There is only write access to this register. Attempting to read the password will report all zeros. The password

cannot be changed while a mission is in progress.

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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

The Full Access Password needs to be transmitted exactly in the sequence FP0, FP1… FP62, FP63. It affects the

functions “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 scratchpad to its memory

location, erase the scratchpad by filling it with new data (write scratchpad command). Otherwise a copy of the

passwords will remain in the scratchpad for public read access.

DATA LOG MEMORY USAGE

Once setup for a mission, the DS1923 logs the temperature measurements and/or humidity at equidistant time

points entry after entry in its data log memory. The data log memory is able to store 8192 entries in 8-bit format or

4096 entries in 16-bit format (Figure 7A). If temperature as well as humidity is 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 different 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 Time Stamp) and the interval between temperature measurements one

can reconstruct the time and date of each measurement.

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 further recording (disable “rollover”) or overwrite the previously recorded

data (enable “rollover”), one entry at a time, starting again at the beginning of the respective memory section. The

contents of the Mission Sample Counter in conjunction with the sample rate and the Mission Time Stamp then

allows 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.

Figure 7A. ONE CHANNEL LOGGING

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

With 16-bit format,

the most-significant

byte is stored at the

lower address.

8192

8-bit entries

Temperature

or

4096

16-bit entries

Temperature

or

Humidity data

2FFFh

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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

Figure 7B. TWO CHANNEL LOGGING, EQUAL RESOLUTION

ETL = EHL = 1

TLFS = HLFS = 0

TLFS = HLFS = 1

1000h

Temperature

4096

Temperature

2048

8-bit entries

16-bit entries

With 16-bit format,

the most-significant

byte is stored at the

lower address.

1FFFh

2000h

1FFFh

2000h

Humidity Data

4096

Humidity Data

2048

8-bit entries

16-bit entries

2FFFh

Figure 7C. TWO CHANNEL LOGGING, DIFFERENT RESOLUTION

ETL = EHL = 1

TLFS = 0; HLFS = 1

TLFS = 1; HLFS = 0

1000h

Temperature

2560

8-bit entries

Temperature

2560

19FFh

1A00h

With 16-bit format,

the most-significant

byte is stored at the

lower address.

16-bit entries

Humidity Data

2560

23FFh

2400h

Humidity Data

2560

16-bit entries

8-bit entries

2DFFh

2E00h

2FFFh

2DFFh

2E00h

2FFFh

(not used)

MISSIONING

The typical task of the DS1923 iButton is recording temperature and/or humidity. Before the device can perform

this function, it needs to be set up properly. This procedure is called missioning.

First of all, DS1923 needs to have its real-time clock set to valid time and date. This reference time may be the

local time, or, when used inside of a mobile unit, UTC (also called GMT, Greenwich Mean Time) or any other time

standard that was agreed upon. The real-time clock oscillator must be running (EOSC = 1). The memory assigned

to store the Mission Time Stamp, Mission Sample Counter, and Alarm Flags must be cleared using the Memory

Clear 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 have to be made in any case, regardless of the type of object to be monitored

and the duration of the mission.

If alarm signaling is desired, the temperature alarm and/or humidity alarm low and high thresholds must be defined.

How to convert a temperature value into the binary code to be written to the threshold registers is described under

“Temperature Conversion” earlier in this document. Determining the thresholds for the humidity alarm is described

in section “Humidity Conversion”. In addition, the temperature and/or humidity alarm must be enabled for the low-

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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

and/or high-threshold. This will make the device respond to a Conditional Search command (see ROM Function

Commands), provided that an alarming condition has been encountered.

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 (single

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 estimated duration of a mission is 10 days (= 14400 minutes), for example,

then the 8192-byte capacity of the data log memory would be sufficient to store a new 8-bit value every 1.8 minutes

(110 seconds). 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.

After the RO bit and the Mission Start Delay are set, the sample rate needs to be written to the Sample Rate

Register. The sample rate may be any value from 1 to 16383, coded as an unsigned 14-bit binary number. A

sample rate of all zeros is not valid and must be avoided under all circumstances. This causes the device to

enter into an unrecoverable state. The fastest sample rate is one sample per second (EHSS = 1, Sample Rate =

0001h) and the slowest is one sample every 273.05 hours (EHSS = 0, Sample Rate = 3FFFh). To get one sample

every 6 minutes, for example, the sample rate value needs to be set to 6 (EHSS = 0) or 360 decimal (equivalent to

0168h at EHSS = 1).

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 needs to be enabled. See Security

by Password for more details.

The last step to begin a mission is to issue the Start Mission command. As soon as it has received this command,

the DS1923 sets the MIP flag and clear 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 time stamp register, and logs the first entry of the mission. This increments both the

Mission Sample Counter and Device Sample Counter. All subsequent log entries are made as specified by the

value in the Sample Rate Register and the EHSS bit.

If the Start Upon Temperature Alarm mode is chosen (SUTA = 1) and temperature logging is enabled (ETL = 1) the

DS1923 first waist until the start delay is over. Then the device wakes up in intervals as specified by the sample

rate and EHSS bit and measure the temperature. This increments the Device Sample Counter only. The first

sample of the mission is logged when the temperature alarm occurred. However, the Mission Sample Counter will

not increment. One sample period later the Mission Time Stamp is set. From then on, both the Mission Sample

Counter and Device Sample Counter increment at the same time. All subsequent log entries will be 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 memory of the DS1923 can be read at any time, e. g., to watch the progress of a mission.

Attempts to read the passwords will read 00h bytes instead of the data that is stored in the password registers.

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 will be written or from which

data will be sent to the master upon a Read command. Register E/S acts like a byte counter and transfer 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 Register 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 offset. If the target address for a Write command is 13Ch, for example, then the scratchpad

stores incoming data beginning at the byte offset 1Ch and is full after only 4 bytes. The corresponding ending offset

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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

in this example is 1Fh. For best economy of speed and efficiency, the target address for writing should point to 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 Partial and Overflow Flag is mainly a means to

support the master checking the data integrity after a Write command. The highest valued bit of the E/S Register,

called AA or Authorization Accepted, indicates that a valid copy command for the scratchpad has been received

and executed. Writing data to the scratchpad clears this flag.

Figure 8. ADDRESS REGISTERS

Bit #

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)

WRITING WITH VERIFICATION

To write data to the DS1923, the scratchpad has to 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 scratchpad 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 correctly 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 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 has to 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 scratchpad. As soon as the DS1923 has received these bytes, it copies

the data to the requested location beginning at the target address.

MEMORY- AND CONTROL-FUNCTION COMMANDS

The “Memory/Control Function Flow Chart” (Figure 9) describes 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 at the end of this document, preceding the Electrical Characteristics section. The

communication between master and DS1923 takes place either at regular speed (default, OD = 0) or at Overdrive

Speed (OD = 1). If not explicitly set into the Overdrive Mode the DS1923 assumes regular speed. Internal memory

access during a mission has priority over external access through the 1-Wire interface. This affects several of the

commands described below. See Memory Access Conflicts for details and remedies.

Write Scratchpad Command [0Fh]

After issuing the Write Scratchpad command, the master must first provide the 2-byte target address, followed by

the data to be written to the scratchpad. The data will be written to the scratchpad starting at the byte offset

(T4:T0). The master has to 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 (see Figure 15) calculates

a CRC of the entire data stream, starting at the command code and ending at the last data byte sent by the master.

27 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

This CRC is generated using the CRC16 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 may send 16 read time slots and will

receive the inverted CRC16 generated by the DS1923.

Note that both register pages are write-protected during a mission. Although the Write Scratchpad command will

work normally at any time, the subsequent copy scratchpad to a register page will fail during a mission.

Read Scratchpad Command [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 will be the target address. The next byte will be the ending offset/data

status byte (E/S) followed by the scratchpad data beginning at the byte offset (T4:T0), as shown in Figure 8. The

master may continue reading data until the end of the scratchpad after which it will receive an inverted CRC16 of

the command code, Target Addresses TA1 and TA2, the E/S byte, and the scratchpad data starting at the target

address. After the CRC is read, the bus master will read logical 1s from the DS1923 until a reset pulse is issued.

Copy Scratchpad with Password [99h]

This command is used to copy data from the scratchpad 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 password. If passwords are

enabled and the transmitted password is different from the stored full-access password, the Copy Scratchpad with

Password command will fail. Then 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 (Authorization Accepted) flag is set and the copy begins. A pattern of alternating 1s

and 0s are 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.

The data to be copied is determined by the three address registers. The scratchpad data from the beginning offset

through the ending offset will be copied, starting at the target address. The AA flag remains at logic 1 until it is

cleared by the next Write Scratchpad command. 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 progress, write attempts

to the register pages will not be successful. The AA bit (Authorization Accepted) remaining at 0 will indicate 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 generates

and transmits a 16-bit CRC following the last data byte of a memory page.

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 passwords. If

passwords are enabled and the transmitted password does not match one of the stored passwords, the Read

Memory with Password and CRC command fails. The device will stop communicating and will wait 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 receive the inverted 16-bit CRC. With subsequent read-data

time slots the master will receive 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.

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 followed by the 2 address bytes and the contents of the data

memory. Subsequent passes through the Read Memory with CRC flow will generate a 16-bit CRC that is the result

of clearing the CRC generator and then shifting in the contents of the data memory page. After the 16-bit CRC of

the last page is read, the bus master receives logical 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.

28 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

Figure 9-1. MEMORY/CONTROL FUNCTION FLOW CHART

From ROM Functions

Master TX Memory or

Control Fkt. Command

Flow Chart (Figure 11)

0FH

Write

AAH

Read

N

Scratchpad

Y

Master TX

Master RX

TA1 (T7:T0)

Master TX

Master RX

TA2 (T15:T8)

DS1923 sets Scratch-

pad Offset = (T4:T0)

and Clears (PF, AA)

Master RX Ending

Offset with Data

Status (E/S)

DS1923 sets Scratch-

pad Offset = (T4:T0)

Master TX Data Byte

to Scratchpad Offset

DS1923 sets (E4:E0)

= Scratchpad Offset

Master RX Data Byte

from Scratchpad Offset

Y

Master

TX Reset?

DS1923 Incre-

ments Scratch-

pad Offset

DS1923 Incre-

ments Scratch-

pad Offset

N

Scratch-

pad Offset =

11111b?

Scratch-

pad Offset =

11111b?

N

Y

N

Y

Partial

Y

Byte Written?

Master RX CRC16 of

Master

Command, Address Data,

PF = 1

E/S Byte, and Data Starting

at the Target Address

N

TX Reset?

N

Master RX CRC16 of

Command, Address Data

Y

Master

TX Reset?

Y

N

Master

TX Reset?

Master RX "1"s

N

Master RX "1"s

To ROM Functions

Flow Chart (Figure 11)

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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

Figure 9-2. MEMORY/CONTROL FUNCTION FLOW CHART

99H

N

Copy Scrpd.

[w/PW]

Y

Master TX

TA1 (T7:T0), TA2 (T15:T8)

Authorization

Code

Master TX

E/S Byte

Master TX

64-Bits [Password]

N

Password

Accepted?

Y

Authorization

Code Match?

Y

AA = 1

DS1923 Copies Scratchpad

Data to Memory

Master

RX "1"s

Copying

Finished

N

Master

TX Reset?

Y

DS1923 TX "0"

Y

Master

TX Reset?

N

DS1923 TX "1"

Master

TX Reset?

N

Y

30 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

Figure 9-3. MEMORY/CONTROL FUNCTION FLOW CHART

69H

N

Read Mem.

[w/PW]&CRC

Y

Master TX

TA1 (T7:T0), TA2 (T15:T8)

Master TX

64-Bits [Password]

Decision made

by DS1923

N

Password

Accepted?

Y

DS1923 sets Memory

Address = (T15:T0)

Decision made

by Master

Master RX Data Byte

from Memory Address

DS1923 Incre-

ments Address

Counter

Y

Master

TX Reset?

N

End of Page?

Y

Master RX CRC16 of

Command, Address, Data

(1^stPass); CRC16 of Data

(Subsequent Passes)

N

Master TX

Reset

CRC OK?

Y

N

End of

Memory?

Y

Master RX "1"s

Master TX

Reset?

N

Y

31 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

Figure 9-4. MEMORY/CONTROL FUNCTION FLOW CHART

96H

55H

N

Y

Clear Mem.

[w/PW]

Forced

Conversion?

Y

Master TX

64-Bits [Password]

FFh dummy byte

Master TX

FFh dummy byte

Mission in

Progress?

N

Password

Accepted?

DS1923 Performs a

Temp. Conversion

Y

DS1923 copies Result

to Address 020C/Dh

Y

Mission in

Progress?

DS1923 Performs a

Humidity Conversion

N

DS1923 clears Mission

Time Stamp, Mission

Samples Counter,

Alarm Flags

DS1923 copies Result

to Address 020E/Fh

N

Master

DS1923 sets

MEMCLR = 1

TX Reset?

Y

N

Master

TX Reset?

Y

32 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

Figure 9-5. MEMORY/CONTROL FUNCTION FLOW CHART

CCH

Start Mission

[w/PW]

33H

N

Stop Mission

[w/PW]

Mission Start

Y

Delay Process

Master TX

64-Bits [Password]

Y

Start Delay

Master TX

Counter = 0?

FFh dummy byte

N

DS1923 Waits for 1 Minute

N

Password

Accepted?

Password

Accepted?

DS1923 decrements

Start Delay Counter

Y

N

Mission in

Progress?

N

Mission in

Progress?

SUTA = 1?

Y

N

DS1923 Sets WFTA=1

DS1923 sets

MIP = 0

N

MEMCLR

= 1?

DS1923 Waits One

Sample Period

WFTA = 0

Y

DS1923 sets

MIP = 1

MIP = 0?

N

Master

N

MEMCLR = 0

TX Reset?

DS1923 Performs 8-bit

Temp. Conversion

DS1923 Initiates

Mission Start Delay

Process

Y

N

Temp.

Alarm?

Y

The Mission

DS1923 sets WFTA=0

and logs first sample

Sample

Counter will

not increment.

DS1923 Waits One

Sample Period

DS1923 copies RTC

Data to Mission Time

Stamp Register

If SUTA = 1,

this is the 2^nd

sample.

N

DS1923 Starts Logging

Taking 1^stSample

Master

TX Reset?

End Of Process

Y

33 of 52

Clear Memory with^DP^Sa¹⁹s²s^3:w^Ho^ygr^rd^och[^r9^o6ⁿh^Te]^{mperature/Humidity Logger iButton with 8kB Data Log Memory}

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 a 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 Clear Memory with Password command will fail.

The device will stop communicating and will wait for a reset pulse. If the password was correct or if passwords

were not enabled, the device will clear the Mission Time Stamp, Mission Sample Counter, 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 execution of the Clear Memory with Password command. Clearing of the data log memory

is not necessary because the Mission Sample Counter indicates how many entries in the data log memory are

valid.

Forced Conversion [55h]

The Forced Conversion command can be used to measure the temperature and humidity without starting a

mission. After the command code the master has to send one FFh byte to get the conversion started. The

conversion result is found as 16-bit value in the Latest Temperature Conversion Result and Latest Humidity

Conversion Result registers. This command is only executed 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 Memory Access Conflicts for details. A forced conversion must not be

attempted while the RTC oscillator is stopped. This causes the device to enter into an unrecoverable state.

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 previous

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 a 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 with

Password command will fail. The device stops communicating 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 Sample Counter does not increment. One sample period later,

the Mission Time Stamp will be 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 will read 1. During a mission there is only

read access to the Register Pages.

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 with Password command will fail. The device stops

communicating 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 restore write access to the Register Pages. The

WFTA bit is not cleared. See the description of the General Status Register for a method to clear the WFTA bit.

MEMORY ACCESS CONFLICTS

While a mission is in progress or while the device is waiting for a temperature alarm to start a mission, periodically

a temperature and/or humidity sample is taken and logged. This "internal activity" has priority over 1-Wire

communication. As a consequence, device-specific commands (excluding ROM function commands and 1-Wire

reset) will 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 device is waiting for a temperature alarm. The table below explains how the remaining

five commands are affected by internal activity, how to detect this interference and how to work around it.

34 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

Command

Indication of Interference

Remedy

Wait 0.5 seconds, 1-Wire reset, address the device,

repeat Write Scratchpad with the same data, and

check the validity of the CRC16 at the end of the

command flow. Alternatively, use Read Scratchpad to

verify data integrity.

The CRC16 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.

The device behaves as if

Wait 0.5 seconds, 1-Wire reset, address the device,

repeat Read Scratchpad, and check the validity of the

CRC16 at the end of the command flow.

Read Scratchpad

Copy Scratchpad

Wait 0.5 seconds, 1-Wire reset, address the device,

authorization code or password issue Read Scratchpad and check the AA-bit of the

was not valid or as if the copy

function would not end.

E/S byte. If the AA-bit is set, Copy Scratchpad was

successful.

The data read changes to all

FFh bytes or all bytes received Wait 0.5 seconds, 1-Wire reset, address the device,

Read Memory with

CRC

are FFh, including the CRC at

the end of the command flow,

despite a valid password.

repeat Read Memory with CRC, and check the validity

of the CRC16 at the end of the memory page.

Wait 0.5 seconds, 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 215h and check the MIP-bit. If the MIP-bit is 0,

Stop Mission was successful.

The general Status register at

address 215h reads FFh or the

MIP bit is 1 while bits 0, 2, and

5 are 0.

Stop Mission

The interference is more likely to be seen with a high sample rate (1 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.

1-WIRE BUS SYSTEM

The 1-Wire bus is a system, which has a single bus master and one or more slaves. In all instances the DS1923 is

a slave device. The bus master is typically a microcontroller. The discussion of this bus system is broken down into

three topics: hardware configuration, transaction sequence, and 1-Wire signaling (signal types and timing). The

1-Wire protocol defines bus transactions in terms of the bus state during specific time slots that are initiated on the

falling edge of sync pulses from the bus master. For a more detailed protocol description, refer to Chapter 4 of the

Book of DS19xx iButton Standards.

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 tri-state

outputs. The 1-Wire port of the DS1923 is open-drain with an internal circuit equivalent to that shown in Figure 10.

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

mode is 15.4kbps and 125kbps in Overdrive. The value of the pullup resistor primarily depends on the network size

and load conditions. The DS1923 requires a pullup resistor of maximum 2.2kꢁ at any speed.

The idle state for the 1-Wire bus is high. If for any reason 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 DS19233 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 conjunction with a DS2480B or DS2490

1-Wire driver and adapters that are based on these driver chips.

35 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

Figure 10. HARDWARE CONFIGURATION

V_PUP

BUS MASTER

DS1923 1-Wire PORT

R_PUP

RX

TX

DATA

RX

TX

5 µA

Typ.

RX = RECEIVE

TX = TRANSMIT

100

ꢁ

Open Drain

Port Pin

MOSFET

TRANSACTION SEQUENCE

The protocol for accessing the DS1923 through the 1-Wire port is as follows:

Cꢀ Initialization

Cꢀ ROM Function Command

Cꢀ Memory/Control Function Command

Cꢀ Transaction/Data

INITIALIZATION

All transactions on the 1-Wire bus begin with an initialization 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 (refer to 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 present 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.

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 exactly matches the 64-bit ROM sequence responds to the

following memory function command. All other slaves will wait for a reset pulse. This command can be used with a

single or multiple devices on the bus.

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 numbers of all slave devices. For each bit of the registration

number, starting with the least significant bit, the 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 second slot,

each slave device participating in the search outputs the complemented value of its registration number 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 participating in the search. If both of the read bits are zero, the master knows that slave

36 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

devices exist with both states of the bit. By choosing which state to write, the bus master branches in the romcode

tree. After one complete pass, the bus master knows the registration number of a single device. Additional passes

identify the registration numbers of the remaining devices. Refer to App Note 187: 1-Wire Search Algorithm for a

detailed discussion, including an example.

Conditional Search [ECh]

The Conditional Search ROM command operates similarly to the Search ROM command except that only those

devices, which 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 individually accessed as if a Match ROM had been issued, since all other devices

have dropped out of the search process and will be waiting for a reset pulse.

The DS1923 responds to the conditional search 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 Temperature Sensor Alarm and

Humidity Alarm). The BOR alarm is always enabled. The first alarm that occurs makes the device respond to the

Conditional Search command.

Skip ROM [CCh]

This command can save time in a single-drop bus system by allowing the bus master to access the memory

functions without providing the 64-bit ROM code. If more than one slave is present on the bus and, for example, 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).

Resume Command [A5h]

The DS1923 needs to 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 has to be repeated for every access. To maximize the data

throughput in a multidrop environment, the Resume function was implemented. This function checks the status of

the RC bit and, if it is set, directly transfers control 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 function. Accessing another device on the bus will clear the RC bit, preventing two or more

devices from simultaneously responding to the Resume Command function.

Overdrive Skip ROM [3Ch]

On a single-drop bus this command can save time by allowing the bus master to access the memory/control func-

tions without providing the 64-bit ROM code. Unlike the normal Skip ROM command, the Overdrive Skip ROM sets

the DS1923 in the Overdrive mode (OD = 1). All communication following this command has to 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 will set all Overdrive-supporting devices into Overdrive mode. To

subsequently address a specific Overdrive-supporting device, a reset pulse at Overdrive speed has to be issued

followed by a Match ROM or Search ROM command 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 will produce a wired-AND result).

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 will respond to the subsequent memory/control

function command. Slaves already in Overdrive mode from a previous Overdrive Skip or successful Overdrive

Match command remains 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.

37 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

Figure 11-1. ROM FUNCTIONS FLOW CHART

Bus Master TX

From Figure 11, 2^ndPart

Reset Pulse

From Memory Functions

Flow Chart (Figure 9)

OD

N

OD = 0

Reset Pulse?

Y

Bus Master TX ROM

DS1923 TX

Function Command

Presence Pulse

To Figure 11

2

^ndPart

33h

55h

F0h

ECh

N

Read ROM

Command?

Match ROM

Command?

Search ROM

Command?

Cond. Search

Command?

N

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

N

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

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

N

Bit 63

Match?

Y

To Figure 11

RC = 1

2

^ndPart

From Figure 11

2

^ndPart

To Memory Functions

Flow Chart (Figure 9)

38 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

Figure 11-2. ROM FUNCTIONS FLOW CHART

To Figure 11, 1^stPart

From Figure 11

1^stPart

CCh

A5h

3Ch

69h

Overdrive Match

ROM?

N

Skip ROM

Command?

Resume

Overdrive

Skip ROM?

Command?

Y

RC = 0

RC = 0 ; OD = 1

N

RC = 1 ?

Y

Master TX Bit 0

Y

N

Master

Bit 0

TX Reset ?

Match?

Y

N

Master TX Bit 1

N

Y

Master

Bit 1

TX Reset ?

Match?

Y

N

Master TX Bit 63

Bit 63

Match?

Y

From Figure 11

1^stPart

RC = 1

To Figure 11

1^stPart

39 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

1-WIRE SIGNALING

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 Presence 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

communicates at standard speed. While in Overdrive Mode the fast timing applies to all waveforms.

To get from idle to active, the voltage on the 1-Wire line needs to fall from V_PUPbelow the threshold V_TL. To get

from active to idle, the voltage needs to rise from V_ILMAXpast the threshold V_TH. The time it takes for the voltage to

make this rise is seen in Figure 12 as 'ꢂ' and its duration depends on the pullup resistor (R_PUP) used and the

capacitance of the 1-Wire network attached. The voltage V_ILMAXis relevant for the DS1923 when determining a

logical level, not triggering any events.

The initialization sequence required to begin any communication 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 the line

for t_RSTL+ t_Fto compensate for the edge. A t_RSTLduration of 690µs or longer will exit the Overdrive Mode returning

the device to standard speed. If the DS1923 is in Overdrive Mode and t_RSTLis no longer than 80µs the devices

remain in Overdrive Mode.

Figure 12. INITIALIZATION PROCEDURE “RESET AND PRESENCE PULSES”

MASTER TX “RESET PULSE” MASTER RX “PRESENCE PULSE”

t_MSP

ꢀ

V_PUP

V_IHMASTER

V_TH

V_TL

V_ILMAX

0V

t_F

t_RSTL

t_PDL

t_RSTH

t_PDH

MASTER

t_REC

RESISTOR

DS1923

After the bus master has released the line it goes into receive mode (RX). Now the 1-Wire bus is pulled to V_PUP

through the pullup resistor or, in case of a DS2480B driver, by active circuitry. When the threshold V_THis crossed,

the DS1923 waits for t_PDHand then transmits a Presence Pulse by pulling the line low for t_PDL. To detect a presence

pulse, the master must test the logical state of the 1-Wire line at t_MSP

.

The t_RSTHwindow must be at least the sum of t_PDHMAX, t_PDLMAX, and t_RECMIN. Immediately after t_RSTHis expired, the

DS1923 is ready for data communication. In a mixed population network t_RSTHshould be extended to minimum

480µs at standard speed and 48µs at Overdrive speed to accommodate other 1-Wire devices.

Read/Write Time Slots

Data communication with the DS1923 takes place in time slots, which 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.

All communication begins with the master pulling the data line low. As the voltage on the 1-Wire line falls below the

threshold V_TL, the DS1923 starts its internal timing generator that determines when the data line is sampled during

a write time slot and how long data will be valid during a read-time slot.

40 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

Master-to-Slave

For a write-one time slot, the voltage on the data line must have crossed the V_THthreshold before the write-one

low time t_W1LMAXis expired. For a write-zero time slot, the voltage on the data line must stay below the V_TH

threshold until the write-zero low time t_W0LMINis expired. The voltage on the data line should not exceed V_ILMAX

during the entire t_W0Lor t_W1Lwindow. After the V_THthreshold has been crossed, the DS1923 needs a recovery time

t_RECbefore it is ready for the next time slot.

Figure 13. READ/WRITE TIMING DIAGRAM

Write-One Time Slot

t_W1L

V_PUP

V_IHMASTER

V_TH

V_TL

V_ILMAX

0V

t_F

ꢀ

t_SLOT

RESISTOR

MASTER

Write-Zero Time Slot

t_W0L

V_PUP

V_IHMASTER

V_TH

V_TL

V_ILMAX

0V

t_REC

t_F

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

t_F

t_REC

DS1923

ꢀ

t_SLOT

RESISTOR

MASTER

41 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

Slave-to-Master

A read-data time slot begins like a write-one time slot. The voltage on the data line must remain below V_TLuntil the

read-low time t_RLis expired. During the t_RLwindow, 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 voltage starts rising as soon as t_RL

is over.

The sum of t_RL+ ꢃ (rise rime) on one side and the internal timing generator of the DS1923 on the other side define

the master sampling window (t_MSRMINto t_MSRMAX) in which the master must perform a read from the data line. For

most reliable communication, t_RLshould be as short as permissible and the master should read close to but no later

than t_MSRMAX. After reading from the data line, the master must wait until t_SLOTis expired. This guarantees sufficient

recovery time t_RECfor the DS1923 to get ready for the next time slot.

Improved Network Behavior

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 sources can also result in signal glitching. A glitch during 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 function command to abort. For better performance in

network 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.

The 1-Wire front end of the DS1923 differs from traditional slave devices in four characteristics.

1) The falling edge of the presence pulse has a controlled 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 parameter t_FPD

,

which has different values for standard and Overdrive speed.

2) There is additional low-pass 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 Overdrive speed.

3) There is a hysteresis at the low-to-high switching threshold V_TH. If a negative glitch crosses V_THbut does not go

below V_TH- V_HY, it will not be recognized (Figure 14, Case A). The hysteresis is effective at any 1-Wire speed.

4) There is a time window specified by the rising edge hold-off time t_REHduring which glitches are ignored, even if

they extend below V_TH- V_HYthreshold (Figure 14, Case B, t_GL< t_REH). Deep-voltage droops or glitches that

appear late after crossing the V_THthreshold and extend beyond the t_REHwindow cannot be filtered out and are

taken as beginning of a new time slot (Figure 14, Case C, t_GLO t_REH).

Only devices that have the parameters t_FPD, V_HY, and t_REHspecified in their electrical characteristics use the

improved 1-Wire front end.

Figure 14. NOISE SUPPRESSION SCHEME

t_REH

V_PUP

V_TH

V_HY

Case A

Case B

Case C

t_GL

0V

t_GL

42 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

CRC GENERATION

With the DS1923 there are two different types of CRCs (Cyclic Redundancy Checks). 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 compare it to the value stored within the DS1923 to determine if the ROM data

has been received error-free. The equivalent polynomial function of this CRC is: X⁸+ X⁵+ X⁴+ 1. This 8-bit CRC is

received in the true (noninverted) form. It is computed at the factory and lasered into the ROM.

The other CRC is a 16-bit type, generated according to the standardized CRC16-polynomial function x¹⁶+ x¹⁵+ x²

+ 1. This CRC is used for error detection when reading register pages or the data log memory 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 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 flow chart 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 flow chart, 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 passes through the Read Memory with CRC flow chart generate

a 16-bit CRC that is the result of clearing the CRC generator and then shifting in the data bytes.

With the Write Scratchpad command the CRC is generated by first clearing the CRC generator and then shifting in

the command code, the Target Addresses, TA1 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 generated by first clearing the CRC generator and then 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 offset. For more information on generating CRC values see the Dallas Application

Note 27.

Figure 15. CRC-16 HARDWARE DESCRIPTION AND POLYNOMIAL

Polynomial = X¹⁶+ X¹⁵+ X²+ 1

1^st

2^nd

3^rd

4^th

5^th

6^th

7^th

8^th

STAGE STAGE

X¹

STAGE STAGE STAGE STAGE STAGE STAGE

X⁰

X²

X³

X⁴

X⁵

X⁶

X⁷

9^th

10^th

11^th

12^th

13^th

14^th

15^th

16^th

STAGE STAGE STAGE STAGE STAGE STAGE STAGE

STAGE

X⁸

X⁹

X¹⁰

X¹¹

X¹²

X¹³

X¹⁴

X¹⁵

X¹⁶

CRC

OUTPUT

INPUT DATA

43 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

Command-Specific 1-Wire Communication Protocol—Legend

Symbol

Description

RST

PD

1-Wire Reset Pulse generated by master

1-Wire Presence Pulse generated by slave

Command and data to satisfy the ROM function protocol

Command "Write Scratchpad"

Select

WS

RS

CPS

RMC

CM

FC

SM

STP

TA

Command "Read Scratchpad"

Command "Copy Scratchpad with Password"

Command "Read Memory with Password & CRC"

Command "Clear Memory with Password "

Command "Forced Conversion"

Command "Start Mission with Password"

Command "Stop Mission with Password"

Target Address TA1, TA2

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 of as many data 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 byte FFh

Transfer of an inverted CRC16

Indefinite loop where the master reads FF bytes

Indefinite loop where the master reads AA bytes

TA-E/S

<32 bytes>

<data>

FFh

CRC16\

FF loop

AA loop

Command-Specific 1-Wire Communication Protocol—Color Codes

Master to slave

Slave to master

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

RST

PD

Select

WS

TA

<data to EOS> CRC16\

FF loop

Read Scratchpad (Cannot Fail)

RST

PD

Select

RS

TA-E/S

<data to EOS> CRC16\

FF loop

Copy Scratchpad with Password (Success)

RST

PD

Select

CPS

TA-E/S

AA loop

44 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

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

RST

PD

Select

CPS

TA-E/S

FF loop

Read Memory with Password and CRC (Success)

RST

PD

Select

RMC

TA

<data to EOP> CRC16\

<32 bytes> CRC16\

FF loop

Loop

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

RST

PD

Select

RMC

TA

FF loop

Clear Memory with Password

RST

PD

Select

CM

FFh

FF loop

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

executed successfully.

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 Sample

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

Start Mission with Password

RST

PD

Select

SM

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

FFh

FF loop

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

successfully.

45 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

MISSION EXAMPLE: PREPARE AND START A NEW MISSION

Assumption: The previous mission has been ended by using the Stop Mission command. Passwords are not

enabled. The device is a DS1923.

Starting a mission requires three steps:

Step 1: clear the data of the previous mission

Step 2: write the setup data to register page 1

Step 3: start the mission

STEP 1

Clear the previous mission.

With only a single device connected to the bus master, the communication of step 1 looks like this:

MASTER MODE

DATA (LSB FIRST)

(Reset)

COMMENTS

TX

RX

TX

RX

Reset pulse

(Presence)

CCh

96h

<8 FFh bytes>

FFh

(Reset)

(Presence)

Presence pulse

Issue “skip ROM” command

Issue “clear memory” command

Send dummy password

Send dummy byte

Reset pulse

Presence pulse

STEP 2

During the setup, the device needs to learn the following information:

Cꢀ Time and Date

Cꢀ Sample Rate

Cꢀ Alarm Thresholds

Cꢀ Alarm Controls (Response to Conditional Search)

Cꢀ General Mission Parameters (e.g., Channels to Log and Logging Format, Rollover, Start Mode)

Cꢀ Mission Start Delay

The following data will setup the DS1923 for a mission that logs temperature and humidity using 8-bit format for

both. Such a mission could last up to 28 days until the 8192-byte data log memory is full.

ADDRESS

0200h

0201h

0202h

0203h

0204h

0205h

0206h

0207h

0208h

0209h

020Ah

020Bh

020Ch

020Dh

020Eh

020Fh

DATA

00h

30h

15h

05h

04h

0Ah

00h

66h

7Ah

6Fh

9Eh

FFh

EXAMPLE VALUES

FUNCTION

15:30:00 hours

Time

Date

15^thof May in 2004

Every 10 minutes (EHSS = 0)

Sample rate

10°C low

Temperature alarm

Threshold

Humidity alarm threshold,

No software correction used

20°C high

40%RH low

70%RH high

(don’t care)

Clock through

Read-only registers

46 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

ADDRESS

0210h

DATA

03h

FFh

EXAMPLE VALUES

FUNCTION

Temperature Alarm Control

Humidity Alarm Control

Enable high and low alarm

0211h

Enable high and low alarm

0212h

01h

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

RTC oscillator control, sample rate

selection

0213h

0214h

0215h

0216h

0217h

0218h

C3h

FFh

5Ah

00h

Normal start; no rollover; 8-bit logging

(don’t care)

General mission control

Clock through

Read-only registers

90 minutes

Mission start delay

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

Write 25 bytes of data to scratchpad

Write through the end of the scratchpad

Reset pulse

0Fh

00h

02h

<25 data bytes>

<7 FFh bytes>

(Reset)

(Presence)

CCh

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

TA2

E/S

(AUTHORIZATION CODE)

02h

1Fh

<8 FFh bytes>

(Reset)

(Presence)

Send dummy password

Reset pulse

Presence pulse

47 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

STEP 3

Start the new mission.

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

<8 FFh bytes>

FFh

(Reset)

(Presence)

Presence pulse

Issue “skip ROM” command

Issue “start mission” command

Send dummy password

Send dummy byte

Reset pulse

Presence pulse

If step 3 was successful, the MIP bit in the General Status Register will be 1, the MEMCLR bit will be 0 and the

mission start delay will count down.

SOFTWARE CORRECTION ALGORITHM FOR TEMPERATURE

The accuracy of high-resolution temperature conversion 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 section Temperature Conversion for the binary number format.

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

The software correction algorithm requires two additional values, which are not stored in the device. For the

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

The correction algorithm consists of two steps, preparation 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 delivered 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.

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

B = (Tr2²- Tr1²) * (Err3 - Err1)/[(Tr2²- Tr1²) * (Tr3 - Tr1) + (Tr3²- Tr1²) * (Tr1 - Tr2)]

A = B * (Tr1 – Tr2) / (Tr2²- Tr1²)

C = Err1 - A * Tr1²- B * Tr1

48 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

Step 2. Execution

Tc = TcH/2 + TcL/512 - Offset

(convert from binary to °C)

(the actual correction)

Tcorr = Tc - (A * Tc²+ B * Tc + C)

Numerical Correction Example

Converted Data from Calibration Memory

Tr2 = -10.1297°C

Error Values

Err2 = 0.0672°C

Err3 = -0.1483°C

Err1 = Err2

Tr3 = 24.6483°C

Tc2 = -10.0625°C

Tc3 = 24.5°C

Resulting Correction Coefficients

B = -0.008741

Application of Correction Coefficients to Sample Reading

Tc = 22.500000°C

A = 0.000175/°C

Tcorr = 22.647275°C

C = -0.039332°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.

SOFTWARE CORRECTION ALGORITHM FOR HUMIDITY

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 different humidity levels, as

shown below. The data is taken at 25°C.

Address

0248h

0249h

024Ah

024Bh

024Ch

024Dh

024Eh

024Fh

0250h

0251h

0252h

0253h

Designator

Hr1H

Hr1L

Description

Low reference humidity, high-byte

Low reference humidity, low-byte

Hc1H

Hc1L

Hr2H

Hr2L

Conversion result at low reference humidity, high-byte

Conversion result at low reference humidity, low-byte

Medium reference humidity, high-byte

Medium reference humidity, low-byte

Hc2H

Hc2L

Hr3H

Hr3L

Conversion result at medium reference humidity, high-byte

Conversion result at medium reference humidity, low-byte

High reference humidity, high-byte

High reference humidity, low-byte

Hc3H

Hc3L

Conversion result at high reference humidity, high-byte

Conversion result at high reference humidity, low-byte

The correction algorithm consists of two steps: preparation and execution. The preparation step first converts

humidity data from binary to decimal %RH format. Next three coefficients A, B, and C are computed. In the

execution 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 corrected 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.

49 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

Step 1. Preparation

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

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

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

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

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

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

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

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

(convert from binary to %RH)

Err1 = Hc1 - Hr1

Err2 = Hc2 - Hr2

Err3 = Hc3 - Hr3

B =

[(Hr2²- Hr1²) * (Err3 - Err1) + Hr3²*(Err1 - Err2) + Hr1² * (Err2 - Err1)]/[(Hr2²- Hr1²) * (Hr3 - Hr1) + (Hr3²-

Hr1²) * (Hr1 - Hr2)]

A =

C =

[Err2 - Err1 + B * (Hr1 - Hr2)] / (Hr2²- Hr1²)

Err1 - A * Hr1²- B * Hr1

Step 2. Execution

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

Hcorr = Hc - (A * Hc²+ B * Hc + C)

(convert from binary to %RH)

(the actual correction)

Numerical Correction Example

Converted Data from Calibration Memory

Hr1 = 20%RH

Error Values

Hr2 = 60%RH

Err1 = -2.35%RH

Err2 = -3.59%RH

Err3 = -0.43%RH

Hr3 = 90%RH

Hc1 = 17.65%RH

Hc2 = 56.41%RH

Hc3 = 89.57%RH

Resulting Correction Coefficients

B = -0.186810

Application of Correction Coefficients to Sample Reading

Hc = 8.9%RH

A = 0.001948/%RH

Hcorr = 9.8%RH

C = 0.607143%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.

50 of 52

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

RH TEMPERATURE COMPENSATION

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.

Temperature compensation uses the following equation:

HTcorr = (Hcorr * K + ꢄ*(T-25°C) - ꢅ*(T-25°C)²)/(K + ꢆ*(T-25°C)- ꢃ*(T-25°C)²)

Hcorr is the humidity reading with the software correction algorithm for humidity already applied, as explained in

the previous section. The function and values of the other parameters are explained in the table below.

Name

Function

Value

T

K

ꢄ

ꢅ

Temperature at the time of humidity conversion

Humidity sensor conversion constant

Linear compensation, enumerator

(in °C)

0.0307

0.0035/°C

0.000043/°C²

Quadratic compensation, enumerator

>15°C: 0.00001/°C

Linear compensation, denominator

ꢆ

?15°C: -0.00005/°C

Quadratic compensation, denominator

0.000002/°C²

ꢃ

Numerical Temperature Compensation Example

Sample Input Data

Application of Correction Coefficients to Sample Reading

ꢆ = 0.00001/°C

T = 70°C

Hcorr = 24.445%RH

HTcorr = (24.445 * 0.0307 + 0.0035 * 45 - 0.000043 * 45²)/ (0.0307

+ 0.00001 * 45 - 0.000002 * 45²)

HTcorr = 30.291 %

SOFTWARE SATURATION DRIFT COMPENSATION

Capacitive humidity sensors read higher humidity values than the actual humidity level when they are exposed to a

high-humidity environment for an extended time period. The DS1923’s humidity sensor produces 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 saturation drift, or sometimes

referred to as hyteresis. This drift is reversible. Readings return to their regular level when the DS1923 is removed

from a high-humidity environment.

It is possible to compensate for most of the error introduced by the saturation drift by post-processing temperature

and humidity logs using the equation below, which is based on laboratory tests and curve-fitting techniques.

N

0.0156 * ARH_k* 2.54^-0.3502*k

^{HScorr = HTcorr -}ꢀ

1 + (T_k- 25) / 100

k = 1

ARH_k

T_k

The average software corrected and temperature compensated humidity reading of the k^thhour that the

device is continuously exposed to 70%RH or higher.

The average software corrected temperature reading of the k^thhour that the device is continuously

exposed to 70%RH or higher.

N

The number of hours that the device is continuously exposed to 70%RH or higher.

HTcorr The humidity reading at the end of the N^thhour with the software correction algorithm for humidity and

temperature compensation already applied. See previous sections for details.

The numbers in the equation are derived from curve fitting. They apply to a time scale in hours.

51 of 52

DS1923: 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_k(°C)

25.1

25.0

24.9

25.0

25.1

25.0

24.9

ARH_k(%RH)

Partial Corrections (individual addends)

1

2

3

4

5

6

7

8

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

HTcorr = 93.70207 %RH

Sum of partial corrections:

3.458875

HScorr

=

HTcorr - Sum of partial corrections

93.70207 %RH - 3.458875%RH

90.24319%RH

The data in this example was taken from devices that were exposed for several hours to 90%RH at 25°C in a 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. Since the error introduced by the saturation is relatively small, for some

applications compensation may not be necessary.

52 of 52


型号：	DS1923-F5
厂家：	DALLAS SEMICONDUCTOR
描述：	Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 温度/湿度记录器iButton ，具有8KB数据记录存储器存储
文件：	总52页 (文件大小：493K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

DS1923-F5 [DALLAS]

相关型号：

DS1923-F5#

DS1923_1

DS1923_11

DS19310

DS1961S

DS1961S-F3

DS1961S-F3

DS1961S-F3#

DS1961S-F3+

DS1961S-F5

DS1961S-F5#

DS1961S-F5+