PIC16F87X
6.1
Timer1 Operation in Timer Mode
6.2
Timer1 Counter Operation
Timer mode is selected by clearing the TMR1CS
(T1CON<1>) bit. In this mode, the input clock to the
timer is FOSC/4. The synchronize control bit T1SYNC
(T1CON<2>) has no effect since the internal clock is
always in sync.
Timer1 may operate in asynchronous or usynchronous
mode depnding on the setting of the TMR1CS bit.
When Timer1 is being incremented via an external
source, increments occur on a rising edge. After
Timer1 is enabled in counter mode, the module must
first have a falling edge before the counter begins to
increment.
FIGURE 6-1: TIMER1 INCREMENTING EDGE
T1CKI
(Default high)
T1CKI
(Default low)
Note: Arrows indicate counter increments.
If T1SYNC is cleared, then the external clock input is
synchronized with internal phase clocks. The synchro-
nization is done after the prescaler stage. The pres-
caler stage is an asynchronous ripple-counter.
6.3
Timer1 Operation in Synchronized
Counter Mode
Counter mode is selected by setting bit TMR1CS. In
this mode, the timer increments on every rising edge of
clock input on pin RC1/T1OSI/CCP2, when bit
T1OSCEN is set, or on pin RC0/T1OSO/T1CKI, when
bit T1OSCEN is cleared.
In this configuration, during SLEEP mode, Timer1 will
not increment even if the external clock is present,
since the synchronization circuit is shut off. The pres-
caler however will continue to increment.
FIGURE 6-2: TIMER1 BLOCK DIAGRAM
Set flag bit
TMR1IF on
Overflow
Synchronized
0
TMR1
clock input
TMR1L
TMR1H
T1OSC
1
TMR1ON
on/off
T1SYNC
(2)
RC0/T1OSO/T1CKI
1
Synchronize
det
Prescaler
1, 2, 4, 8
T1OSCEN
Enable
Oscillator
FOSC/4
Internal
Clock
0
(1)
(2)
RC1/T1OSI/CCP2
2
Q Clock
T1CKPS1:T1CKPS0
TMR1CS
Note 1: When the T1OSCEN bit is cleared, the inverter is turned off. This eliminates power drain.
2: For the PIC16F873/876, the Schmitt Trigger is not implemented in external clock mode.
DS30292B-page 52
1999 Microchip Technology Inc.
ETC [ ETC ]
