ADT7485A

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8

Table 3. 16−Byte DIB Details

Byte

Name

Value

Description

0

Device

Capabilities

0xc0

Fixed address

device

1

Version/Revision

0x10

Meets Version 1 of

SST specification

2, 3

Vendor ID

00x11d

4

Contains company

ID number in little

endian format

4, 5

Device ID

0x7485

Contains device ID

number in little

endian format

6

Device Interface

0x01

SST device

7

Function

Interface

0x00

Reserved

8

Reserved

0x00

Reserved

9

Reserved

0x00

Reserved

10

Reserved

0x00

Reserved

11

Reserved

0x00

Reserved

12

Reserved

0x00

Reserved

13

Reserved

0x00

Reserved

14

Revision ID

0x05

Contains revision ID

15

Client Device

Address

0x48 to

0x4a

Dependent on the

state of address pin

Ping()

The Ping() command verifies if a device is responding at

a particular address. The ADT7485A shows a valid

non−zero FCS in response to the Ping() command when

correctly addressed.

Table 4. Ping() Command

Target Address

Write Length

Read Length

FCS

(Not necessary)

0x00

0x00

ResetDevice()

This command resets the register map and conversion

controller. The reset command can be global or directed at

the client address of the ADT7485A.

Table 5. ResetDevice() Command

Target Address

Write

Length

Read

Length

Reset

Command

FCS

Device Address

0x01

0x00

0xf6

GetIntTemp()

The ADT7485A shows the local temperature of the device

in response to the GetIntTemp() command. The data has a

little endian, 16−bit, twos complement format.

GetExtTemp()

Prompted by the GetExtTemp() command, the ADT7485A

shows the temperature of the remote diode in little endian,

16−bit, twos complement format. The ADT7485A shows

0x8000 in response to this command if the external diode is

an open or short circuit.

GetAllTemps()

The ADT7485A shows the local and remote temperatures

in a 4−byte block of data (internal temperature first,

followed by external temperature) in response to a

GetAllTemps() command.

SetExtOffset()

This command sets the offset that the ADT7485A will use

to correct errors in the external diode. The offset is set in little

endian, 16−bit, twos complement format. The maximum

offset is

±128°C with +0.25°C resolution.

GetExtOffset()

This command causes the ADT7485A to show the offset

that it is using to correct errors in the external diode. The

offset value is returned in little endian format, that is, LSB

before MSB.

ADT7485A Response to Unsupported Commands

A full list of command codes supported by the

ADT7485A is given in Table 2. The offset registers

(Command Code 0xe0) are the only registers that the user

can write to. The other defined registers are read only.

Writing to Register Addresses 0x02, 0x09, and 0x15 to 0xdf

shows a valid FSC, but no action is taken by the ADT7485A.

The ADT7485A shows an invalid FSC if the user attempts

to write to the device between Command Codes 0xe2 to

0xee. These registers are reserved for the manufacturer’s use

only, and no data can be written to the device via these

addresses.

Voltage Measurement

The ADT7485A has four external voltage measurement

Pins 5 and 8 measure the supplies of the 12 V, 5.0 V,

chip−set supply voltage in a computer system.

Analog−to−Digital Converter

All analog inputs are multiplexed into the on−chip,

successive approximation, analog−to−digital converter

(ADC). This has a resolution of 10 bits. The basic input

range is 0 V to 2.25 V, but the inputs have built−in

attenuators to allow measurement of 2.5 V, 3.3 V, 5.0 V,

external components.

To allow for the tolerance of these supply voltages, the

ADC produces a specific output for each nominal input

voltage and therefore has adequate headroom to cope with

overvoltage. The full−scale voltage that can be recorded for

each channel is shown in Table 6.