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PIC16F87XA

DS39582B-page 58

2003 Microchip Technology Inc.

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.

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.

FIGURE 6-1:

TIMER1 INCREMENTING EDGE

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.

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

T1CKI

(Default High)

T1CKI

(Default Low)

Note: Arrows indicate counter increments.

TMR1H

TMR1L

T1OSC

T1SYNC

TMR1CS

T1CKPS1:T1CKPS0

Q Clock

T1OSCEN

Enable

Oscillator(1)

FOSC/4

Internal

Clock

TMR1ON

On/Off

Prescaler

1, 2, 4, 8

Synchronize

det

Synchronized

Clock Input

RC0/T1OSO/T1CKI

RC1/T1OSI/CCP2(2)

Note 1: When the T1OSCEN bit is cleared, the inverter is turned off. This eliminates power drain.

Set Flag bit

TMR1IF on

Overflow

TMR1

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