PIC16F677T-ESS データシートの表示（PDF） - Microchip Technology

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PIC16F677T-ESS

20-Pin Flash-Based, 8-Bit CMOS Microcontrollers with nanoWatt Technology

Microchip Technology 

PIC16F631/677/685/687/689/690

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.

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.

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

FOSC/4

0

T0CKI

pin

T0SE

1

0

T0CS

1

8-bit

Prescaler

WDTE

SWDTEN

31 kHz

INTOSC

8

PSA

Watchdog

Timer

16-bit

Prescaler 16

PS<2:0>

WDTPS<3:0>

Note 1: T0SE, T0CS, PSA, PS<2:0> are bits in the OPTION register.

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

3: WDTE bit is in the Configuration Word register.

1

Sync 2

cycles

0

PSA

Data Bus

8

TMR0

Set Flag bit T0IF

on Overflow

1

WDT

Time-out

0

PSA

© 2008 Microchip Technology Inc.

DS41262E-page 81

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