Data Sheet

ADT7470

Rev. E | Page 29 of 40

DETAILED REGISTER DESCRIPTIONS

Table 24. Register 0x20 to Register 0x29. Temperature Reading Registers (Power-On Default = 0x00).

Register

Address

Read/Write

Description

Comments

0x20

Read-only

8-bit Temperature 1 reading (from TMP05 sensor).

Bit[7] = Sign bit, indicates if temperature is positive or

0x21

Read-only

8-bit Temperature 2 reading (from TMP05 sensor).

negative

0x22

Read-only

8-bit Temperature 3 reading (from TMP05 sensor).

Bits[6:0] = temperature result

0x23

Read-only

8-bit Temperature 4 reading (from TMP05 sensor).

0x24

Read-only

8-bit Temperature 5 reading (from TMP05 sensor).

To calculate the temperature:

0x25

Read-only

8-bit Temperature 6 reading (from TMP05 sensor).

Positive Temperature = ADC Code (decimal)

0x26

Read-only

8-bit Temperature 2 reading (from TMP05 sensor).

Negative Temperature = ADC (decimal) minus 256

0x27

Read-only

8-bit Temperature 3 reading (from TMP05 sensor).

0x28

Read-only

8-bit Temperature 4 reading (from TMP05 sensor).

0x29

Read-only

8-bit Temperature 5 reading (from TMP05 sensor).

Readings from daisy-chained TMP05 are processed and loaded into the temperature reading registers.

Table 25. Register 0x2A to Register 0x31. Fan Tach Reading Registers (Power-On Default = 0x00).

Register Address

Read/Write

Description

0x2A

Read-only

Tach 1 low byte (8 MSBs of reading).

0x2B

Read-only

Tach 1 high byte (8 LSBs of reading).

0x2C

Read-only

Tach 2 high byte (8 MSBs of reading).

0x2D

Read-only

Tach 2 low byte (8 LSBs of reading).

0x2E

Read-only

Tach 3 high byte (8 MSBs of reading).

0x2F

Read-only

Tach 3 low byte (8 LSBs of reading).

0x30

Read-only

Tach 4 high byte (8 MSBs of reading).

0x31

Read-only

Tach 4 low byte (8 LSBs of reading).

The fan tach reading registers shown in Table 25 count the number of 11.11 µs periods (based on an internal 90 kHz clock) that occur

between a number of consecutive fan tach pulses (default = 2). The number of tach pulses used to count can be changed using the fan

pulses per revolution register (Register 0x43). This allows the fan speed to be accurately measured. Because a valid fan tachometer

reading requires that two bytes are read, the low byte must be read first. Both the low and high bytes are then frozen until read. At power-

on, these registers contain 0x0000 until such time as the first valid fan tach measurement is read in to these registers. This prevents false

interrupts from occurring while the fans are spinning up.

A count of 0xFFFF indicates that a fan is

•

Stalled or blocked (object jamming the fan).

•

Failed (internal circuitry destroyed).

•

Not populated. The ADT7470 expects to see a fan connected to each tach. If a fan is not connected to that tach,

its tach minimum high and low byte are set to 0xFFFF.

Table 26. Register 0x32 to Register 0x35. Current PWM Duty Cycle Registers (Power-On Default = 0xFF).

Register Address

Read/Write

Description

0x32

Read/Write

PWM1 current duty cycle (0% to 100% duty cycle = 0x00 to 0xFF).

0x33

Read/Write

PWM2 current duty cycle (0% to 100% duty cycle = 0x00 to 0xFF).

0x34

Read/Write

PWM3 current duty cycle (0% to 100% duty cycle = 0x00 to 0xFF).

0x35

Read/Write

PWM4 current duty cycle (0% to 100% duty cycle = 0x00 to 0xFF).

The current PWM duty cycle registers, shown in Table 26, reflect the PWM duty cycle driving each fan at any given time. When in

automatic fan speed control mode, the ADT7470 reports the PWM duty cycles back through these registers. The PWM duty cycle values

vary according to temperature in automatic fan speed control mode. During fan startup, these registers report back 0x00. In manual fan

control mode, the PWM duty cycle outputs can be set to any duty cycle value by writing to these registers.