Datasheet

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 2T
OSC (and
a small RC delay of 20 ns) and low for at least 2T
OSC
(and a small RC delay of 20 ns). Refer to the electrical
specification of the desired device.
REGISTER 4-1: 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 R/W-1 R/W-1 R/W-1 R/W-1 R/W-1 R/W-1 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