
MCV18E
DS41399A-page 14
2009 Microchip Technology Inc.
2.2.2.2
OPTION Register
The OPTION register is a readable and writable
register, which 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 Timer0 register, assign the prescaler
to the Watchdog Timer.
REGISTER 2-2:
OPTION_REG: OPTION REGISTER
R/W-1
RBPU
INTEDG
T0CS
T0SE
PSA
PS2
PS1
PS0
bit 7
bit 0
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
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: Timer0 Clock Source Select bit
1
= Transition on RA4/T0CKI pin
0
= Internal instruction cycle clock (FOSC/4)
bit 4
T0SE: Timer0 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
PS<2:0>: Prescaler Rate Select bits
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
Timer0 Rate
WDT Rate