Datasheet

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.