PIC16F870_13 Datasheet, PDF (50/172 Pages) Microchip Technology – 28/40-Pin, 8-Bit CMOS FLASH Microcontrollers

PIC16F870/871
6.1 Timer1 Operation in Timer 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.
FIGURE 6-1:
TIMER1 INCREMENTING EDGE
6.2 Timer1 Counter Operation
Timer1 may operate in either a Synchronous, or an
Asynchronous 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.
T1CKI
(Default High)
T1CKI
(Default Low)
Note: Arrows indicate counter increments.
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, when bit T1OSCEN is
set, or on pin RC0/T1OSO/T1CKI, when bit T1OSCEN
is cleared.
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.
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 6-2:
TIMER1 BLOCK DIAGRAM
Set Flag bit
TMR1IF on
Overflow
RC0/T1OSO/T1CKI
RC1/T1OSI
TMR1
0
Synchronized
Clock Input
TMR1H TMR1L
1
T1OSC
TMR1ON
On/Off
T1SYNC
T1OSCEN _FOSC/4
Enable
Oscillator⁽¹⁾
Internal
Clock
1
Prescaler
1, 2, 4, 8
0
2
T1CKPS1:T1CKPS0
Synchronize
det
Q Clock
TMR1CS
Note 1: When the T1OSCEN bit is cleared, the inverter is turned off. This eliminates power drain.
DS30569C-page 50
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