SSC050-01 datasheet(39/79 Pages) MAXIM

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4-23

Control Registers

SSC050-01

Control Register Definition

Data Sheet

Revision 4.0

November 10, 2004

32h: Fan Speed Current Count 0 (FSCC0)

FSCC0

Address:

32h

Reset Value:

0000_0000b

Description

Fan Speed Current Count 0.

This register affects pin P P2.4.

76543

210

Fan Speed Current Count

Bit(s)

Bit Label

Access

Description

FSCO7-0

These eight bits, when enabled by setting the FSCEN bit in the FSC0 register pro-

vide the user with an accurate binary fan speed count value which can be used to

determine the current RPM value of the fan. A minimum of one complete revolution

of the fan is required to generate an accurate fan speed count value. The following

equation can be used to determine the current RPM value of the fan:

RPM = (1,200,000)/(Decimal-Count-Value X Divisor)

When the result of a read of this register is 00h, an accurate fan speed count value

has not been generated indicating that the fan has not completed a minimum of one

revolution. When the result of a read of this register is FFh, the fan is rotating very

slowly or there are no tachometer pulses present. When operating in a polled mode

with the FSIEN bit reset in the FSC0 register, this register will automatically update

with an accurate fan speed count once per revolution of the fan. When operating in

an interrupt mode with the FSIEN bit set in the FSC0 register, this register will auto-

matically update with an accurate fan speed count once per revolution of the fan until

an interrupt is generated. Once the interrupt is generated, the value will remain sta-

ble until the interrupt is cleared. When the interrupt is cleared, this register will also

be cleared indicating that a valid RPM value is in the process of being generated.

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