PC87366 datasheet(128/240 Pages) NSC

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5.0 Fan Speed Monitor (Continued)

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5.3.2

Fan Monitor Threshold Register (FMTHR)

This 8-bit register contains the programmable threshold for the fan. This threshold is the maximum number of clock cycles

between consecutive tachometer pulses (frequencies of 16, 8, 4 or 2 KHz). It represents the minimum fan speed permitted

in the system. If the period between consecutive tachometer pulses is greater than the threshold, an interrupt (if enabled) is

issued. After reset, the value of FMTHR is FFh.

This register should not be changed when the corresponding Fan Monitor Enable bit is set to 1 (enabled), since this may

cause unpredictable results.

Location:

Device specific

Type:

R/W

5.3.3

Fan Monitor Speed Register (FMSPR)

This read-only 8-bit register holds the speed reading, represented by number of clock cycles between consecutive tachom-

eter pulses. For details, refer to Section 5.2. When the Speed Ready bit of the FMCSR register is 1, FMSPR holds valid data

that has not yet been read.

It is cleared to 00h upon any of the following conditions:

System reset

Fan Monitor Enable bit is set to 0

Overﬂow bit is set to 1.

Location:

Device specific

Type:

5.3.4

Fan Monitor Control and Status Register (FMCSR)

Location:

Device specific

Type:

Varies per bit

Bit

76543210

Name

Threshold Value

Reset

11111111

Bit

76543210

Name

Fan Speed Reading

Reset

00000000

Bit

76543210

Name

Reserved

Clock Select

Filter

Disable

Interrupt

Enable

Overﬂow

Over

Threshold

Speed

Ready

Reset

00100000

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