EMC6D103 datasheet(45/89 Pages) SMSC

45 / 89 page

Fan Control Device with High Frequency PWM Support and Hardware Monitoring Features

Datasheet

SMSC EMC6D103

Revision 0.4 (04-04-05)

DATASHEET

7.1.4.6

Programming Options for Each Tachometer Input

The features defined in this section are programmable via the TACHx Option registers located at

offsets 90h-93h and the PWMx Option registers located at offsets 94h-96h.

TACH READING UPDATE TIME

In Mode 1, the Fan Tachometer Reading registers are continuously updated. In Mode 2, the fan

tachometer registers are updated every 300ms, 500msec, or 1000msec. This option is programmed

via bits[1:0] in the PWMx Option register. The PWM associated with a particular TACH(s) determines

the TACH update time.

PROGRAMMED NUMBER OF TACH EDGES

In modes 1 & 2, the number of edges is programmable for 2, 3, 5 or 9 edges (i.e., ½ tachometer pulse,

1 tachometer pulse, 2 tachometer pulses, 4 tachometer pulses). This option is programmed via bits[2:1]

in the TachX Option register.

Note: The “5 edges” case corresponds to two tachometer pulses, or 1 RPM for most fans. Using

the other edge options will require software to scale the values in the reading register to

correspond to the count for 1 RPM.

GUARD TIME (MODE 2 ONLY)

The guard time is programmable from 8 to 63 clocks (90kHz). This option is programmed via bits[4:3]

in the TachX Option register.

IGNORE FIRST 3 TACHOMETER EDGES (MODE 2 ONLY)

Option to ignore first 3 tachometer edges after guard time. This option is programmed for each

tachometer via bits[2:0] in the TACHx Option register. Default is do not ignore first 3 tachometer edges

after guard time.

7.1.4.7

Summary of Operation for Modes 1 & 2

The following summarizes the detection cases:

■

No edge occurs during the PWM ‘ON’ time: indicate this condition as a stalled fan

−The tachometer reading register contains FFFFh.

■

One edge (or less than programmed number of edges) occurs during the PWM ‘ON’ time :

indicate this condition as a slow fan.

−If the SLOW bit is set to 0, the tachometer reading register will be set to FFFEh to indicate that

this is a slow fan instead of a seized fan. Note: This operation also pertains to the case where the

tachometer counter reaches FFFFh before the programmed number of edges occurs.

−If the SLOW bit is set to one, the tachometer reading register will be set to FFFFh. In this case,

no distinction is made between a slow or seized fan.

Note: The Slow Interrupt feature (SLOW) is configured in the TACHx Options registers at offsets 90h

to 93h.

■

The programmed number of edges occurs:

-Mode 1: If the programmed number of edges occurs before the counter reaches FFFFh latch the

tachometer count

-Mode 2: If the programmed number of edges occurs during the PWM ‘ON’ time: latch the

tachometer count. (see Note below).

Notes:

■

Whenever the programmed number of edges is detected, the edge detection ends and the state

machine is reset. The tachometer reading register is updated with the tachometer count value at

this time. See Note 7.1 below for the one exception to this behavior.

EMC6D103 Datasheet(PDF) 45 Page - SMSC Corporation

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