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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