12F629 datasheet(30/136 Pages) MICROCHIP

30 / 136 page

PIC12F629/675

DS41190G-page 30

 2010 Microchip Technology Inc.

4.3

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 accom-

plished 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 2TOSC (and

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

(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 ANSEL (9Fh) and CMCON (19h)

registers must be initialized to configure an

analog channel as a digital input. Pins

configured as analog inputs will read ‘0’.

The ANSEL register is defined for the

PIC12F675.

R/W-1

GPPU

INTEDG

T0CS

T0SE

PSA

PS2

PS1

PS0

bit 7

bit 0

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

bit 7

GPPU: GPIO Pull-up Enable bit

1 = GPIO pull-ups are disabled

0 = GPIO pull-ups are enabled by individual PORT latch values

bit 6

INTEDG: Interrupt Edge Select bit

1 = Interrupt on rising edge of GP2/INT pin

0 = Interrupt on falling edge of GP2/INT pin

bit 5

T0CS: TMR0 Clock Source Select bit

1 = Transition on GP2/T0CK pin

0 = Internal instruction cycle clock (CLKOUT)

bit 4

T0SE: TMR0 Source Edge Select bit

1 = Increment on high-to-low transition on GP2/T0CKI pin

0 = Increment on low-to-high transition on GP2/T0CKI pin

bit 3

PSA: Prescaler Assignment bit

1 = Prescaler is assigned to the WDT

0 = Prescaler is assigned to the TIMER0 module

bit 2-0

PS2:PS0: Prescaler Rate Select bits

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

12F629 Datasheet(PDF) 30 Page - Microchip Technology

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