Temperature Value Registers
The registers in the ADT7481 are eight bits wide. These
registers are used to store the results of remote and local
temperature measurements, high and low temperature limits,
and to configure and control the device. A description of these
Address Pointer Register
The address pointer register does not have, nor does it
require, an address because the first byte of every write
operation is automatically written to this register. The data
in this first byte always contains the address of another
register on the ADT7481, which is stored in the address
pointer register. It is to this register address that the second
byte of a write operation is written to, or to which a
subsequent read operation is performed.
The power−on default value of the address pointer register
is 0x00, so if a read operation is performed immediately after
power−on, without first writing to the address pointer, the
value of the local temperature will be returned since its
register address is 0x00.
The ADT7481 has five registers to store the results of
local and remote temperature measurements. These
registers can only be written to by the ADC and read by the
user over the SMBus.
The local temperature value register is at Address 0x00.
The Remote 1 temperature value high byte register is at
Address 0x01, with the Remote 1 low byte register at
The Remote 2 temperature value high byte register is at
Address 0x30, with the Remote 2 low byte register at
The Remote 2 temperature values can also be read from
Address 0x01 for the high byte, and Address 0x10 for the
low byte if Bit 3 of Configuration Register 1 is set to 1.
To read the Remote 1 temperature values, set Bit 3 of
Configuration Register 1 to 0.
The power−on default value for all five registers is 0x00.
Table 4. Configuration 1 Register (Read Address 0x03, Write Address 0x09)
Setting this bit to 1 masks all ALERTs on the ALERT pin. Default = 0 = ALERT enabled. This applies only if Pin 8 is
configured as ALERT, otherwise it has no effect.
Setting this bit to 1 places the ADT7481 in standby mode, that is, it suspends all temperature measurements
(ADC). The SMBus remains active and values can be written to, and read from, the registers. However THERM
and ALERT are not active in standby mode, and their states in standby mode are not reliable.
Default = 0 = temperature monitoring enabled.
This bit selects the function of Pin 8. Default = 0 = ALERT. Setting this bit to 1 configures Pin 8 as the THERM2 pin.
Reserved for future use.
Setting this bit to 1 enables the user to read the Remote 2 values from the Remote 1 registers. When default = 0,
Remote 1 temperature values and limits are read from these registers.
Setting this bit to 1 enables the extended temperature measurement range of
to +191°C. When using the
default = 0, the temperature range is 0°C to +127°C.
Setting this bit to 1 masks ALERTs due to the Remote 1 temperature exceeding a programmed limit. Default = 0.
Setting this bit to 1 masks ALERTs due to the Remote 2 temperature exceeding a programmed limit. Default = 0.
Table 5. Configuration 2 Register (Address 0x24)
Setting this bit to 1 locks all lockable registers to their current values. This prevents tampering with settings until
the device is powered down. Default = 0.
Reserved for future use.
Conversion Rate/Channel Selector Register
The conversion rate/channel selector register for reads is
at Address 0x04, and at Address 0x0A for writes. The four
LSBs of this register are used to program the conversion
times from 15.5 ms (Code 0x0A) to 16 seconds (Code
0x00). To program the ADT7481 to perform continuous
measurements, set the conversion rate register to 0x0B. For
example, a conversion rate of eight conversions/second
means that beginning at 125 ms intervals, the device
performs a conversion on the local and the remote
This register can be written to, and read back from, the
SMBus. The default value of this register is 0x08, giving a
rate of 16 conversions per second. Using slower conversion
times greatly reduces the device power consumption.
Bit 7 in this register can be used to disable averaging of the
temperature measurements. All temperature channels are
measured by default. It is possible to configure the
ADT7481 to measure the temperature of one channel only.
This can be configured using Bit 4 and Bit 5 (see Table 6).
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