ADT7461A

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9

Table 3. Temperature Data Format

(Temperature High Byte)

Temperature

Binary

Offset Binary (Note 1)

–55°C

0 000 0000

(Note 2)

0 000 1001

0°C

0 000 0000

0 100 0000

+1°C

0 000 0001

0 100 0001

+10°C

0 000 1010

0 100 1010

+25°C

0 001 1001

0 101 1001

+50°C

0 011 0010

0 111 0010

+75°C

0 100 1011

1 000 1011

+100°C

0 110 0100

1 010 0100

+125°C

0 111 1101

1 011 1101

+127°C

0 111 1111

1 011 1111

+150°C

0 111 1111

(Note 3)

1 101 0110

1. Offset binary scale temperature values are offset by 64°C.

2. Binary scale temperature measurement returns 0°C for all

temperatures < 0°C.

3. Binary scale temperature measurement returns 127°C for all

temperatures > 127°C.

The user can switch between measurement ranges at any

time. Switching the range likewise switches the data format.

The next temperature result following the switching is

reported back to the register in the new format. However, the

contents of the limit registers do not change. It is up to the

user to ensure that when the data format changes, the limit

registers are reprogrammed as necessary. More information

on this is found in the Limit Registers section.

ADT7461A Registers

The ADT7461A contains 22, 8−bit registers in total.

These registers store the results of remote and local

temperature measurements, high and low temperature

limits, and configure and control the device. See the Address

Pointer Register section through the Consecutive ALERT

Register section of this data sheet for more information on

the ADT7461A registers. Additional details are shown in

Table 4 through Table 8. The entire register map is available

in Table 9.

Address Pointer Register

The address pointer register itself 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 ADT7461A that is stored in the address

pointer register. It is to this register address that the second

byte of a write operation is written, or to which a subsequent

read operation is performed.

The power−on default value of the address pointer register

is 0x00. Therefore, if a read operation is performed

immediately after power−on, without first writing to the

address pointer, the value of the local temperature is returned

because its register address is 0x00.

Temperature Value Registers

The ADT7461A has three registers to store the results of

local and remote temperature measurements. These

registers can only be written to by the ADC and can be read

by the user over the SMBus. The local temperature value

register is at Address 0x00.

The external temperature value high byte register is at

Address 0x01, with the low byte register at Address 0x10.

The power−on default for all three registers is 0x00.

Configuration Register

The configuration register is Address 0x03 at read and

Address 0x09 at write. Its power−on default is 0x00. Only

four bits of the configuration register are used. Bit 0, Bit 1,

Bit 3, and Bit 4 are reserved; the user does not write to them.

Bit 7 of the configuration register masks the ALERT

output. If Bit 7 is 0, the ALERT output is enabled. This is the

power−on default. If Bit 7 is set to 1, the ALERT output is

disabled. This applies only if Pin 6 is configured as ALERT.

If Pin 6 is configured as THERM2, then the value of Bit 7

has no effect.

If Bit 6 is set to 0, which is power−on default, the device

is in operating mode with ADC converting. If Bit 6 is set to

1, the device is in standby mode and the ADC does not

convert. The SMBus does, however, remain active in

standby mode; therefore, values can be read from or written

to the ADT7461A via the SMBus. The ALERT and THERM

outputs are also active in standby mode. Changes made to

the registers in standby mode that affect the THERM or

ALERT outputs cause these signals to be updated.

Bit 5 determines the configuration of Pin 6 on the

ADT7461A. If Bit 5 is 0 (default), then Pin 6 is configured

as an ALERT output. If Bit 5 is 1, then Pin 6 is configured

as a THERM2 output. Bit 7, the ALERT mask bit, is only

active when Pin 6 is configured as an ALERT output. If Pin

6 is set up as a THERM2 output, then Bit 7 has no effect.

Bit 2 sets the temperature measurement range. If Bit 2 is

0 (default value), the temperature measurement range is set

between 0

°C to +127°C. Setting Bit 2 to 1 sets the

measurement range to the extended temperature range

(−64

°C to +191°C).

Table 4. Configuration Register Bit Assignments

Bit

Name

Function

Power−On

Default

7

MASK1

0 = ALERT Enabled

1 = ALERT Masked

0

6

RUN/STOP

0 = Run

1 = Standby

0

5

ALERT/

THERM2

0 = ALERT

1 = THERM2

0

4, 3

Reserved

0

2

Temperature

Range Select

0 = 0°C to 127°C

1 = Extended range

0

1, 0

Reserved

0