PIC12F635ESS datasheet(63/234 Pages) MICROCHIP

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DS41232D-page 61

PIC12F635/PIC16F636/639

5.0

TIMER0 MODULE

The Timer0 module is an 8-bit timer/counter with the

following features:

• 8-bit timer/counter register (TMR0)

• 8-bit prescaler (shared with Watchdog Timer)

• Programmable internal or external clock source

• Programmable external clock edge selection

• Interrupt on overflow

Figure 5-1 is a block diagram of the Timer0 module.

5.1

Timer0 Operation

When used as a timer, the Timer0 module can be used

as either an 8-bit timer or an 8-bit counter.

5.1.1

8-BIT TIMER MODE

When used as a timer, the Timer0 module will

increment every instruction cycle (without prescaler).

Timer mode is selected by clearing the T0CS bit of the

OPTION register to ‘0’.

When TMR0 is written, the increment is inhibited for

two instruction cycles immediately following the write.

5.1.2

8-BIT COUNTER MODE

When used as a counter, the Timer0 module will

increment on every rising or falling edge of the T0CKI

pin. The incrementing edge is determined by the T0SE

bit of the OPTION register. Counter mode is selected by

setting the T0CS bit of the OPTION register to ‘1’.

FIGURE 5-1:

BLOCK DIAGRAM OF THE TIMER0/WDT PRESCALER

Note:

The value written to the TMR0 register can

be adjusted, in order to account for the two

instruction cycle delay when TMR0 is

written.

T0CKI

T0SE

TMR0

Watchdog

Timer

WDT

Time-out

PS<2:0>

WDTE

Data Bus

Set Flag bit T0IF

on Overflow

T0CS

Note

T0SE, T0CS, PSA, PS<2:0> are bits in the OPTION register.

SWDTEN and WDTPS<3:0> are bits in the WDTCON register.

WDTE bit is in the Configuration Word register.

8-bit

Prescaler

FOSC/4

PSA

16-bit

Prescaler

WDTPS<3:0>

31 kHz

INTOSC

SWDTEN

Sync

2 TCY

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