Preliminary Technical Data

ADT7420

Rev. PrA | Page 13 of

REGISTERS

The ADT7420 contains 14 registers:

•

Nine temperature registers

•

A status register

•

An ID register

•

A configuration register

•

An address pointer register

•

A software reset

All registers are eight bits wide. The temperature value registers,

the status register, and the ID register are read-only. The software

reset is a write-only register. On power-up, the address pointer

register is loaded with 0x00 and points to the temperature value

register MSB.

Table 6. ADT7420 Registers

Register

Address

Description

Power-On

Default

0x00

Temperature value most significant byte

0x00

0x01

Temperature value least significant byte

0x00

0x02

Status

0x00

0x03

Configuration

0x00

0x04

0x20 (64°C)

0x05

0x00 (64°C)

0x06

0x05 (10°C)

0x07

0x00 (10°C)

0x08

0x49 (147°C)

0x09

0x80 (147°C)

0x0A

0x05 (5°C)

0x0B

ID

0xCX

0x2F

Software reset

0xXX

ADDRESS POINTER REGISTER

This register is always the first register written to during a write

to the ADT7420. It should be set to the address of the register

to which the write or read transaction is intended. Table 7

shows the register address of each register on the ADT7420.

The default value of the address pointer register is 0x00.

Table 7. Address Pointer Register

P7

P6

P5

P4

P3

P2

P1

P0

ADD7

ADD6

ADD5

ADD4

ADD3

ADD2

ADD1

ADD0

TEMPERATURE VALUE REGISTERS

The temperature value most significant byte (MSB) and tem-

perature value least significant byte (LSB) registers store the

temperature measured by the internal temperature sensor.

The temperature is stored in twos complement format with

the MSB being the temperature sign bit. When reading from

these registers, the eight MSBs (Bit 7 to Bit 15) are read first

from Register Address 0x00 and then the eight LSBs (Bit 0 to

Bit 7) are read from Register Address 0x01. Only the tempera-

ture value most significant byte (Register Address 0x00) needs to

be loaded into the address pointer register because the address

pointer autoincrements to the temperature value least signifi-

cant byte address (Register Address 0x01).

the ADC is configured to convert the temperature to a 16-bit

digital value, then Bit 0 to Bit 2 are no longer used as flag bits

and are instead used as the LSB bits for the extended digital value.

Table 8. Temperature Value MSB Register (Register Address 0x00)

Bit

Default Value

Type

Name

Description

[8:14]

0000000

R

Temp

Temperature value in twos complement format

15

0

R

Sign

Sign bit, indicates if the temperature value is negative or positive

Table 9. Temperature Value LSB Register (Register Address 0x01)

Bit

Default

Value

Type

Name

Description

0

0

R

T

Flags a T

resolution). When the temperature value is below T

Contains the Least Significant Bit 0 of the 15-bit temperature value if the configuration

register, Register Address 0x03[7] = 1 (16-bit resolution).

1

0

R

T

Flags a T

resolution). When the temperature value is above T

Contains the Least Significant Bit 1 of the 15-bit temperature value if the configuration

register, Register Address 0x03[7] = 1 (16-bit resolution).

2

0

R

T

Flags a T

resolution). When the temperature value exceeds T

Contains the Least Significant Bit 2 of the 15-bit temperature value if the configuration

register, Register Address 0x03[7] = 1 (16-bit resolution).

[3:7]

00000

R

Temp

Temperature value in twos complement format.