PIC16C71 datasheet(68/337 Pages) MICROCHIP

68 / 337 page

PIC16C6X

DS30234D-page 68

7.3

Prescaler

An 8-bit counter is available as a prescaler for the

Timer0 module or as a postscaler for the Watchdog

Timer (WDT), respectively (Figure 7-6). For simplicity,

this counter is being referred to as “prescaler” through-

out this data sheet. Note that the prescaler may be

used by either the Timer0 module or the Watchdog

Timer, but not both. Thus, a prescaler assignment for

the Timer0 module means that there is no prescaler for

the Watchdog Timer, and vice-versa.

Applicable Devices

61 62 62A R62 63 R63 64 64A R64 65 65A R65 66 67

The PSA and PS2:PS0 bits (OPTION<3:0>) determine

the prescaler assignment and prescale ratio.

When assigned to the Timer0 module, all instructions

writing to the TMR0 register (e.g. CLRF

TMR0,

MOVWF TMR0, BSF TMR0,bitx

) will clear the pres-

caler count. When assigned to the Watchdog Timer, a

CLRWDT

instruction will clear the Watchdog Timer and

the prescaler count. The prescaler is not readable or

writable.

Note:

Writing to TMR0 when the prescaler is

assigned to Timer0 will clear the prescaler

count, but will not change the prescaler

assignment.

FIGURE 7-6:

BLOCK DIAGRAM OF THE TIMER0/WDT PRESCALER

RA4/T0CKI

T0SE

CLKOUT (=Fosc/4)

SYNC

Cycles

TMR0 reg

8-bit Prescaler

8 - to - 1MUX

M U X

Watchdog

Timer

PSA

WDT

Time-out

PS2:PS0

Note: T0CS, T0SE, PSA, PS2:PS0 are (OPTION<5:0>).

PSA

WDT Enable bit

Data Bus

Set ﬂag bit T0IF

on Overﬂow

PSA

T0CS

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