MEC1322 datasheet(281/456 Pages) MICROCHIP

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DS00001719D-page 281

MEC1322

24.11.1

TACHX CONTROL REGISTER

Offset

00h

Bits

Description

Type

Default

Reset

Event

31:16 TACHX_COUNTER

This 16-bit field contains the latched value of the internal Tach pulse

counter, which may be configured by the Tach Reading Mode Select

field to operate as a free-running counter or to be gated by the Tach

input signal.

If the counter is free-running (Mode 0), the internal Tach counter

increments (if enabled) on transitions of the raw Tach input signal

and is latched into this field every time it is incremented. The act of

reading this field will not reset the counter, which rolls over to 0000h

after FFFFh. The firmware will compute the delta between the current

count reading and the previous count reading, to determine the num-

ber of pulses detected over a programmed period.

If the counter is gated by the Tach input and clocked by 100kHz_Clk

(Mode 1), the internal counter will be latched into the reading register

when the programmed number of edges is detected or when the

counter reaches FFFFh. The internal counter is reset to zero after it

is copied into this register.

Note:

In Mode 1, a counter value of FFFFh means that the Tach

did not detect the programmed number of edges in

655ms. A stuck fan can be detected by setting the TACHx

High Limit Register to a number less than FFFFh. If the

internal counter then reaches FFFFh, the reading register

will be set to FFFFh and an out-of-limit interrupt can be

sent to the EC.

R00h

VCC1_

RESET

15 TACH_INPUT_INT_EN

1=Enable Tach Input toggle interrupt from Tach block

0=Disable Tach Input toggle interrupt from Tach block

R/W

VCC1_

RESET

14 COUNT_READY_INT_EN

1=Enable Count Ready interrupt from Tach block

0=Disable Count Ready interrupt from Tach block

R/W

VCC1_

RESET

13 Reserved

12:11 TACH_EDGES

A Tach signal is a square wave with a 50% duty cycle. Typically, two

Tach periods represents one revolution of the fan. A Tach period con-

sists of three Tach edges.

This programmed value represents the number of Tach edges that

will be used to determine the interval for which the number of

100kHz_Clk pulses will be counted

11b=9 Tach edges (4 Tach periods)

10b=5 Tach edges (2 Tach periods)

01b=3 Tach edges (1 Tach period)

00b=2 Tach edges (1/2 Tach period)

R/W

00b

VCC1_

RESET

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