PIC16F946 Datasheet, PDF (86/274 Pages) Microchip Technology – 64-Pin Flash-Based, 8-Bit CMOS Microcontrollers with LCD Driver and nanoWatt Technology

PIC16F946
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.
REGISTER 5-1:
OPTION_REG – OPTION REGISTER (ADDRESS: 81h OR 181h)
R/W-1 R/W-1 R/W-1 R/W-1 R/W-1 R/W-1 R/W-1
RBPU INTEDG T0CS
T0SE
PSA
PS2
PS1
bit 7
R/W-1
PS0
bit 0
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2-0
RBPU: PORTB Pull-up Enable bit
1 = PORTB pull-ups are disabled
0 = PORTB pull-ups are enabled by individual port latch values in WPUA register
INTEDG: Interrupt Edge Select bit
1 = Interrupt on rising edge of RB0/INT/SEG0 pin
0 = Interrupt on falling edge of RB0/INT/SEG0 pin
T0CS: TMR0 Clock Source Select bit
1 = Transition on RA4/C1OUT/T0CKI/SEG4 pin
0 = Internal instruction cycle clock (CLKO)
T0SE: TMR0 Source Edge Select bit
1 = Increment on high-to-low transition on RA4/C1OUT/T0CKI/SEG4 pin
0 = Increment on low-to-high transition on RA4/C1OUT/T0CKI/SEG4 pin
PSA: Prescaler Assignment bit
1 = Prescaler is assigned to the WDT
0 = Prescaler is assigned to the Timer0 module
PS<2:0>: Prescaler Rate Select bits
Bit Value TMR0 Rate WDT Rate⁽¹⁾
000
1:2
1:1
001
1:4
1:2
010
1:8
1:4
011
1 : 16
1:8
100
1 : 32
1 : 16
101
1 : 64
1 : 32
110
1 : 128 1 : 64
111
1 : 256 1 : 128
Note 1: A dedicated 16-bit WDT postscaler is available for the PIC16F946. See
Section 16.6 “Watchdog Timer (WDT)” for more information.
Legend:
R = Readable bit
- n = Value at POR
W = Writable bit
‘1’ = Bit is set
U = Unimplemented bit, read as ‘0’
‘0’ = Bit is cleared x = Bit is unknown
DS41265A-page 84
Preliminary
© 2005 Microchip Technology Inc.