PIC12F635/PIC16F636/639
2.2.2.2
OPTION Register
Note:
To achieve a 1:1 prescaler assignment for
Timer0, assign the prescaler to the WDT by
setting the PSA bit of the OPTION register
to ‘1’. See Section 5.1.3 “Software
Programmable Prescaler”.
The OPTION register is a readable and writable
register which contains various control bits to
configure:
• TMR0/WDT prescaler
• External RA2/INT interrupt
• TMR0
• Weak pull-up/pull-downs on PORTA
REGISTER 2-2:
OPTION_REG: OPTION REGISTER
R/W-1
RAPU
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 7
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
RAPU: PORTA Pull-up Enable bit
1= PORTA pull-ups are disabled
0= PORTA 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.
DS41232D-page 27
MICROCHIP [ MICROCHIP ]
