PIC16F722-ESLASHML datasheet(117/302 Pages) MICROCHIP

117 / 302 page

DS41341E-page 117

PIC16F72X/PIC16LF72X

12.3

Timer1 Prescaler

Timer1 has four prescaler options allowing 1, 2, 4 or 8

divisions of the clock input. The T1CKPS bits of the

T1CON register control the prescale counter. The

prescale counter is not directly readable or writable;

however, the prescaler counter is cleared upon a write to

TMR1H or TMR1L.

12.4

Timer1 Oscillator

A dedicated low-power 32.768 kHz oscillator circuit is

built-in between pins T1OSI (input) and T1OSO

(amplifier output). This internal circuit is to be used in

conjunction with an external 32.768 kHz crystal.

The oscillator circuit is enabled by setting the

T1OSCEN bit of the T1CON register. The oscillator will

continue to run during Sleep.

12.5

Timer1 Operation in

Asynchronous Counter Mode

If control bit T1SYNC of the T1CON register is set, the

external clock input is not synchronized. The timer

increments asynchronously to the internal phase

clocks. If external clock source is selected then the

timer will continue to run during Sleep and can

generate an interrupt on overflow, which will wake-up

the processor. However, special precautions in

software are needed to read/write the timer (see

Section 12.5.1 “Reading and Writing Timer1 in

Asynchronous Counter Mode”).

12.5.1

READING AND WRITING TIMER1 IN

ASYNCHRONOUS COUNTER

MODE

Reading TMR1H or TMR1L while the timer is running

from an external asynchronous clock will ensure a valid

read (taken care of in hardware). However, the user

should keep in mind that reading the 16-bit timer in two

8-bit values itself, poses certain problems, since the

timer may overflow between the reads.

For writes, it is recommended that the user simply stop

the timer and write the desired values. A write

contention may occur by writing to the timer registers,

while the register is incrementing. This may produce an

unpredictable value in the TMR1H:TMR1L register

pair.

Note:

The oscillator requires a start-up and

stabilization

time

before

use.

Thus,

T1OSCEN should be set and a suitable

delay observed prior to enabling Timer1.

Note:

When switching from synchronous to

asynchronous operation, it is possible to

skip an increment. When switching from

asynchronous to synchronous operation,

it is possible to produce an additional

increment.

PIC16F722-E/ML Datasheet(PDF) 117 Page - Microchip Technology

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