ADT7481

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9

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

registers follows.

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.

Temperature Value Registers

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.

Address 0x01, with the Remote 1 low byte register at

Address 0x10.

Address 0x30, with the Remote 2 low byte register at

Address 0x33.

Address 0x01 for the high byte, and Address 0x10 for the

low byte if Bit 3 of Configuration Register 1 is set to 1.

Configuration Register 1 to 0.

Table 4. Configuration 1 Register (Read Address 0x03, Write Address 0x09)

Bit

Mnemonic

Function

7

Mask

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.

6

Mon/STBY

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.

5

AL/TH

This bit selects the function of Pin 8. Default = 0 = ALERT. Setting this bit to 1 configures Pin 8 as the THERM2 pin.

4

Reserved

Reserved for future use.

3

Remote

1/2

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.

2

Temp

Range

Setting this bit to 1 enables the extended temperature measurement range of −64°C to +191°C. When using the

default = 0, the temperature range is 0°C to +127°C.

1

Mask R1

Setting this bit to 1 masks ALERTs due to the Remote 1 temperature exceeding a programmed limit. Default = 0.

0

Mask R2

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)

Bit

Mnemonic

Function

7

Lock Bit

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.

<6:0>

Res

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

temperature channels.

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).