PIC16F818/819
7.2
Timer1 Operation in Timer Mode
7.4
Timer1 Operation in Synchronized
Counter Mode
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.
Counter mode is selected by setting bit TMR1CS. In
this mode, the timer increments on every rising edge of
clock input on pin RB7/T1OSI/PGD when bit
T1OSCEN is set, or on pin RB6/T1OSO/T1CKI/PGC
when bit T1OSCEN is cleared.
7.3
Timer1 Counter Operation
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
prescaler stage is an asynchronous ripple counter.
Timer1 may operate in Asynchronous or Synchronous
mode depending 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.
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 prescaler,
however, will continue to increment.
FIGURE 7-1:
TIMER1 INCREMENTING EDGE
T1CKI
(Default High)
T1CKI
(Default Low)
Note: Arrows indicate counter increments.
FIGURE 7-2:
TIMER1 BLOCK DIAGRAM
Set Flag bit
TMR1IF on
Overflow
Synchronized
0
TMR1
Clock Input
TMR1L
TMR1H
1
TMR1ON
On/Off
T1SYNC
T1OSC
1
Synchronize
det
Prescaler
1, 2, 4, 8
RB6/T1OSO/T1CKI/PGC
RB7/T1OSI/PGD
T1OSCEN
Enable
FOSC/4
Internal
Clock
0
(1)
Oscillator
2
Q Clock
T1CKPS1:T1CKPS0
TMR1CS
Note 1: When the T1OSCEN bit is cleared, the inverter is turned off. This eliminates power drain.
DS39598E-page 58
2004 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
