
2001 Microchip Technology Inc.
DS35007B-page 9
PIC16F84A
2.3.2
OPTION REGISTER
The OPTION register is a readable and writable
register which contains various control bits to configure
the TMR0/WDT prescaler, the external INT interrupt,
TMR0, and the weak pull-ups on PORTB.
REGISTER 2-2:
OPTION REGISTER (ADDRESS 81h)
Note:
When
the
prescaler
is
assigned
to
the WDT (PSA = ’1’), TMR0 has a 1:1
prescaler assignment.
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 pin
0
= Internal instruction cycle clock (CLKOUT)
bit 4
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
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
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
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