Maxim Integrated MAX31782 - Manual (Page 92)

MaximIntegrated 10-4
MAX31782 User’s Guide
Revision 0; 8/11
10.2.1TachometerControlRegister(TACHCNn)
The tachometer control register, TACHCNn, is used to set up and start the tachometer, and is also where tachometer
interrupt flags are located . It should be noted that the user should not modify the reserved bits in the TACHCNn regis-
ters . Otherwise, undesired operation can occur .
BIT NAME DESCRIPTION
15 — Reserved . The user should not write to this bit .
14:13 TRPS[1:0]
Revolution Prescaler . These bits are used to set the number of tachometer pin falling edges are
required to trigger a capture . This allows the tachometer to easily work with fans that produce mul-
tiple pulses per revolution .
TRPS[1:0] PRESCALER
00 1 pulse per revolution
01 2 pulses per revolution
10 4 pulses per revolution
11 8 pulses per revolution
12:11 — Reserved . The user should not write to these bits .
10:9 TPS[2:0]
Clock Prescale . These bits select the frequency of the clock input to the tachometer . The tachom-
eter clock is a divided version of the system clock . The TPS[2:0] bits should be configured by
the user when the timer is stopped (TACHE = 0) . While hardware does not prevent changing the
TPS[2:0] bits when the timer is running, the resultant behavior is nondeterministic .
TPS[2:0] TACHOMETERINPUTCLOCK
000 Sysclk/1
001 Sysclk/4
010 Sysclk/16
011 Sysclk/64
100 Sysclk/256
101 Sysclk/1024
11x Sysclk/1
7 TF
Overflow Flag . This bit is set when the tachometer’s TACHV register overflows from FFFFh to 0000h .
An interrupt will be generated if TACHIE=1 . This flag must be cleared by software .
6 TEXF
External Tachometer Trigger Flag . A falling edge on the tachometer’s pin (TACH .n) causes this flag
to be set if enabled (TEXEN = 1) . The TEXF flag is only set once the tachometer revolution prescal-
er condition is met . This flag must be cleared by software . Setting this bit to 1 forces a tachometer
interrupt if enabled .
Note1: The revolution prescaler always triggers on the first tachometer pulse received, then,
depending on division factor, it triggers again after 1, 2, 4, or 8 tachometer pulses .
Note2:This flag is set on a falling edge of the tachometer pin even if the tachometer is disabled
(TACHE = 0) .
5:4 — Reserved . The user should not write to these bits .
3 TEXEN
External Enable . Setting this bit to 1 enables the capture function on a falling edge of the tachom-
eter pin (TACH .n) .
2 TACHE
Run Control . This bit enables the tachometer operation when set to 1 . Clearing this bit to 0 halts the
tachometer operation and preserves the current count in TACHV .
1 TACHIE Enable Tachometer Interrupt . Setting this bit to 1 enables the interrupt from the TF and TEXF flags .
0 — Reserved . The user should not write to this bit .
Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Name — TRPS .1 TRPS .0 — — TPS .2 TPS .1 TPS .0 TF TEXF — — TEXEN TACHE TACHIE —
Reset 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1
Access r rw rw r r rw rw rw rw rw r r rw rw rw r