Datasheet

PIC16F87/88
DS30487D-page 18  2002-2013 Microchip Technology Inc.
2.2.2.2 OPTION_REG Register
The OPTION_REG register is a readable and writable
register that contains various control bits to configure
the TMR0 prescaler/WDT postscaler (single assign-
able register known also as the prescaler), the external
INT interrupt, TMR0 and the weak pull-ups on PORTB.
REGISTER 2-2: OPTION_REG: OPTION CONTROL REGISTER (ADDRESS 81h, 181h)
Note: To achieve a 1:1 prescaler assignment for
the TMR0 register, assign the prescaler to
the Watchdog Timer. Although the pres-
caler can be assigned to either the WDT or
Timer0, but not both, a new divide counter
is implemented in the WDT circuit to give
multiple WDT time-out selections. This
allows TMR0 and WDT to each have their
own scaler. Refer to Section 15.12
“Watchdog Timer (WDT)” for further
details.
R/W-1 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 PS0
bit 7 bit 0
bit 7 RBPU
: PORTB Pull-up Enable bit
1 = PORTB pull-ups are disabled
0 = PORTB pull-ups are enabled by individual port latch values
bit 6 INTEDG: Interrupt Edge Select bit
1 = Interrupt on rising edge of RB0/INT pin
0 = Interrupt on falling edge of RB0/INT pin
bit 5 T0CS: TMR0 Clock Source Select bit
1 = Transition on RA4/T0CKI/C2OUT pin
0 = Internal instruction cycle clock (CLKO)
bit 4 T0SE: TMR0 Source Edge Select bit
1 = Increment on high-to-low transition on RA4/T0CKI/C2OUT pin
0 = Increment on low-to-high transition on RA4/T0CKI/C2OUT 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 PS<2:0>: Prescaler Rate Select bits
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 Value TMR0 Rate WDT Rate
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