PIC12F635ESLASHSS datasheet(56/196 Pages) MICROCHIP

56 / 196 page

PIC12F635/PIC16F636/639

DS41232B-page 54

Preliminary

5.3

Using Timer0 with an External

Clock

When no prescaler is used, the external clock input is the

same as the prescaler output. The synchronization of

T0CKI, with the internal phase clocks, is accomplished

by sampling the prescaler output on the Q2 and Q4

cycles of the internal phase clocks. Therefore, it is

necessary for T0CKI to be high for at least 2 TOSC (and a

small RC delay of 20 ns) and low for at least 2 TOSC (and

a small RC delay of 20 ns). Refer to the electrical

specification of the desired device.

OPTION_REG – OPTION REGISTER (ADDRESS: 81h)

Note:

The CMCON0 (19h) register must be ini-

tialized to configure an analog channel as

a digital input. Pins configured as analog

inputs will read ‘0’.

R/W-1

RAPU

INTEDG

T0CS

T0SE

PSA

PS2

PS1

PS0

bit 7

bit 0

bit 7

RAPU: PORTA Pull-up Enable bit

= PORTA pull-ups are disabled

= PORTA pull-ups are enabled by individual values in the WPUDA register

bit 6

INTEDG: Interrupt Edge Select bit

= Interrupt on rising edge of RA2/T0CKI/INT/C1OUT pin

= Interrupt on falling edge of RA2/T0CKI/INT/C1OUT pin

bit 5

T0CS: TMR0 Clock Source Select bit

= Transition on RA2/T0CKI/INT/C1OUT pin

= Internal instruction cycle clock (CLKOUT)

bit 4

T0SE: TMR0 Source Edge Select bit

= Increment on high-to-low transition on RA2/T0CKI/INT/C1OUT pin

= Increment on low-to-high transition on RA2/T0CKI/INT/C1OUT pin

bit 3

PSA: Prescaler Assignment bit

= Prescaler is assigned to the WDT

= Prescaler is assigned to the Timer0 module

bit 2-0

PS<2:0>: Prescaler Rate Select bits

Note 1: A dedicated 16-bit WDT postscaler is available for the PIC12F635/PIC16F636/639.

See Section 12.11 “Watchdog Timer (WDT)” for more information.

Legend:

R = Readable bit

W = Writable bit

U = Unimplemented bit, read as ‘0’

- n = Value at POR

‘1’ = Bit is set

‘0’ = Bit is cleared

x = Bit is unknown

000

001

010

011

100

101

110

111

1 : 2

1 : 4

1 : 8

1 : 16

1 : 32

1 : 64

1 : 128

1 : 256

1 : 1

1 : 2

1 : 4

1 : 8

1 : 16

1 : 32

1 : 64

1 : 128

Bit Value

TMR0 Rate WDT Rate(1)

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