PIC16F870SLASHP datasheet(52/156 Pages) MICROCHIP

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PIC16F870/871

DS30569A-page 52

Preliminary

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 asynchronous or usynchronous

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, 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 pres-

caler 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 pres-

caler 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

T1CKPS<1:0>

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(2)

Note 1:

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

2: For the PIC16F870/871, the Schmitt Trigger is not implemented in external clock mode.

Set flag bit

TMR1IF on

Overflow

TMR1

(2)

PIC16F870/P Datasheet(PDF) 52 Page - Microchip Technology

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