PIC16F87 Datasheet, PDF (20/214 Pages) Microchip Technology – 18/20/28-Pin Enhanced FLASH Microcontrollers with nanoWatt Technology

PIC16F87/88
2.2.2.2 OPTION Register
The OPTION register is a readable and writable regis-
ter that contains various control bits to configure the
TMR0 prescaler/WDT postscaler (single assignable
register known also as the prescaler), the external INT
interrupt, TMR0, and the weak pull-ups on PORTB.
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 selection. This
allows TMR0 and WDT to each have their
own scaler. Refer to Section 15.12
“Watchdog Timer (WDT)” for further
details.
REGISTER 2-2:
OPTION REGISTER (ADDRESS 81h, 181h)
R/W-1
R/W-1
R/W-1
R/W-1 R/W-1
RBPU INTEDG T0CS
T0SE
PSA
bit 7
R/W-1
PS2
R/W-1
PS1
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
INTEDG: Interrupt Edge Select bit
1 = Interrupt on rising edge of RB0/INT pin
0 = Interrupt on falling edge of RB0/INT pin
T0CS: TMR0 Clock Source Select bit
1 = Transition on RA4/T0CKI pin
0 = Internal instruction cycle clock (CLKO)
T0SE: TMR0 Source Edge Select bit
1 = Increment on high-to-low transition on RA4/T0CKI pin
0 = Increment on low-to-high transition on RA4/T0CKI 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
000
001
010
011
100
101
110
111
TMR0 Rate WDT Rate
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
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
DS30487B-page 18
Preliminary
 2003 Microchip Technology Inc.