ADT7460ARQ-REEL Datasheet, PDF (33/47 Pages) ON Semiconductor – Remote Thermal Monitor and Fan Controller

ADT7460
Table 45. FAN TACHOMETER READING REGISTERS (POWER-ON DEFAULT = 0X00) (Note 1)
Register Address
R/W
Description
0x28
Read-only TACH1 Low Byte
0x29
Read-only TACH1 High Byte
0x2A
Read-only TACH2 Low Byte
0x2B
Read-only TACH2 High Byte
0x2C
Read-only TACH3 Low Byte
0x2D
Read-only TACH3 High Byte
0x2E
Read-only TACH4 Low Byte
0x2F
Read-only TACH4 High Byte
1. The Fan Tachometer Reading registers count the number of 11.11 ms 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 (Reg. 0x7B). This allows the fan speed to be accurately measured. Since 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 ADT7460 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 should be set to 0xFFFF.)
• Alternate function, for example, TACH4 reconfigured as a THERM pin.
• 2-wire Instead of 3-wire Fan
Table 46. CURRENT PWM DUTY CYCLE REGISTERS (POWER-ON DEFAULT = 0XFF) (Note 1)
Register Address
R/W
Description
0x30
R/W
PWM1 Current Duty Cycle (0% to 100% Duty Cycle = 0x00 to 0xFF).
0x31
R/W
PWM2 Current Duty Cycle (0% to 100% Duty Cycle = 0x00 to 0xFF).
0x32
R/W
PWM3 Current Duty Cycle (0% to 100% Duty Cycle = 0x00 to 0xFF).
1. These registers reflect the PWM duty cycle driving each fan at any given time. When in automatic fan speed control mode, the ADT7460
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 software mode, the PWM duty cycle outputs can be set to any duty
cycle value by writing to these registers.
Table 47. OPERATING POINT REGISTERS (POWER-ON DEFAULT = 0X64) (Note 1)
Register Address
R/W
Description
0x33
R/W
Remote 1 Operating Point Register (Default = 100°C)
0x34
R/W
Local Temp Operating Point Register (Default = 100°C)
0x35
R/W
Remote 2 Operating Point Register (Default = 100°C)
1. These registers become read-only when the Configuration Register 1 lock bit is set to 1. Any subsequent attempts to write to these registers
will fail. These registers set the target operating point for each temperature channel when the dynamic T_MIN control feature is enabled. The
fans being controlled are adjusted to maintain temperature about an operating point.
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