PIC12F675T-ESLASHP datasheet(33/136 Pages) MICROCHIP

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DS41190G-page 33

PIC12F629/675

5.1

Timer1 Modes of Operation

Timer1 can operate in one of three modes:

• 16-bit timer with prescaler

• 16-bit synchronous counter

• 16-bit asynchronous counter

In Timer mode, Timer1 is incremented on every

instruction cycle. In Counter mode, Timer1 is

incremented on the rising edge of the external clock

input T1CKI. In addition, the Counter mode clock can

be synchronized to the microcontroller system clock

or run asynchronously.

In counter and timer modules, the counter/timer clock

can be gated by the T1G input.

If an external clock oscillator is needed (and the

microcontroller is using the INTOSC w/o CLKOUT),

Timer1 can use the LP oscillator as a clock source.

5.2

Timer1 Interrupt

The Timer1 register pair (TMR1H:TMR1L) increments

to FFFFh and rolls over to 0000h. When Timer1 rolls

over, the Timer1 interrupt flag bit (PIR1<0>) is set. To

enable the interrupt on rollover, you must set these bits:

• Timer1 interrupt Enable bit (PIE1<0>)

• PEIE bit (INTCON<6>)

• GIE bit (INTCON<7>).

The interrupt is cleared by clearing the TMR1IF in the

Interrupt Service Routine.

5.3

Timer1 Prescaler

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

divisions of the clock input. The T1CKPS bits

(T1CON<5:4>) 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.

FIGURE 5-2:

TIMER1 INCREMENTING EDGE

Note:

In Counter mode, a falling edge must be

registered by the counter prior to the first

incrementing rising edge.

Note:

The TMR1H:TTMR1L register pair and the

TMR1IF bit should be cleared before

enabling interrupts.

T1CKI =

when TMR1

Enabled

T1CKI =

when TMR1

Enabled

Note 1: Arrows indicate counter increments.

2: In Counter mode, a falling edge must be registered by the counter prior to the first incrementing rising edge of the

clock.

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