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706679 Rev 09-26-18
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MFR_SPECIFIC_02 0xD2 – Fan Tachometer Count, Read Word
This command returns a word value (low byte first) of the fan tachometer pulse count per second. The user
should know what the pulse per revolution specification is for the fan that is installed, in order to translate this
value into an actual RPM value.
If the tachometer signal is interrupted by pulse-width modulating the fan power, then the returned tachometer
pulse count per second value is only valid when the fan is powered at 100% duty cycle (continuous power). A
fan with an open collector tachometer output may still fail to provide a low output when the fan input power is
off. A four-terminal fan with a separate power and PWM inputs might provide an accurate tachometer signal at
any speed.
The coefficient parameters used to translate the data to the actual pulse count per second information are given
below.
Parameter Value
m
1d
b
0
R
0
Table 13 PMBus direct format coefficient parameters for MFR_SPECIFIC_02
