PIC16F688
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 5.1.3 “Software
Programmable Prescaler”.
The OPTION register 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
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
DS41203D-page 14
© 2007 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
