PIC16F631/677/685/687/689/690
2.2.2.2
OPTION Register
Note:
To achieve a 1:1 prescaler assignment for
Timer0, assign the prescaler to the WDT by
setting PSA bit of the OPTION register to
‘1’. See Section 6.3 “Timer1 Prescaler”.
The OPTION register, shown in Register 2-2, is a
readable and writable register, which contains various
control bits to configure:
• Timer0/WDT prescaler
• External RA2/INT interrupt
• Timer0
• Weak pull-ups on PORTA/PORTB
REGISTER 2-2:
OPTION_REG: OPTION REGISTER
R/W-1
RABPU
bit 7
R/W-1
R/W-1
T0CS
R/W-1
T0SE
R/W-1
PSA
R/W-1
PS2
R/W-1
PS1
R/W-1
PS0
INTEDG
bit 0
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
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2-0
RABPU: PORTA/PORTB Pull-up Enable bit
1= PORTA/PORTB pull-ups are disabled
0= PORTA/PORTB pull-ups are enabled by individual PORT latch values
INTEDG: Interrupt Edge Select bit
1= Interrupt on rising edge of RA2/INT pin
0= Interrupt on falling edge of RA2/INT pin
T0CS: Timer0 Clock Source Select bit
1= Transition on RA2/T0CKI pin
0= Internal instruction cycle clock (FOSC/4)
T0SE: Timer0 Source Edge Select bit
1= Increment on high-to-low transition on RA2/T0CKI pin
0= Increment on low-to-high transition on RA2/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
Timer0 Rate WDT Rate
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
© 2007 Microchip Technology Inc.
DS41262D-page 37
MICROCHIP [ MICROCHIP ]
