MEC1404 Datasheet, PDF (372/572 Pages) Microchip Technology – Keyboard and Embedded Controller Products for Notebook PC

MEC140X/1X
26.11.1 TACHX CONTROL REGISTER
Offset ^00h
Bits
Description
Type
31:16 TACHX_COUNTER
R
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
TACHx input signal.
If the counter is free-running (Mode 0), the internal Tach counter
increments (if enabled) on transitions of the raw TACHx 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 TACHx input and clocked by 100kHz_-
Clk (Mode 1), the internal counter will be latched into the reading reg-
ister 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
Tachometer logic 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.
15 TACH_INPUT_INT_EN
R/W
1=Enable TACHx Input toggle interrupt from Tachometer block
0=Disable TACHx Input toggle interrupt from Tachometer block
14 COUNT_READY_INT_EN
R/W
1=Enable Count Ready interrupt from Tachometer block
0=Disable Count Ready interrupt from Tachometer block
13 Reserved
R
12:11 TACH_EDGES
R/W
A tachometer signal is a square wave with a 50% duty cycle. Typi-
cally, two tachometer periods represents one revolution of the fan. A
tachometer period consists of three edges.
This programmed value represents the number of tachometer 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)
Default
00h
Reset
Event
nSYSR
ST
0b
nSYSR
ST
0b
nSYSR
ST
-
-
00b
nSYSR
ST
DS00001956D-page 372
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