
PIC12F508/509/16F505
DS41236E-page 24
2009 Microchip Technology Inc.
4.5
OPTION Register
The OPTION register is a 8-bit wide, write-only register,
which contains various control bits to configure the
Timer0/WDT prescaler and Timer0.
By executing the OPTION instruction, the contents of
the W register will be transferred to the OPTION regis-
ter. A Reset sets the OPTION<7:0> bits.
Note:
If TRIS bit is set to ‘0’, the wake-up on
change and pull-up functions are disabled
for that pin (i.e., note that TRIS overrides
Option
control
of
GPPU/RBPU
and
GPWU/RBWU).
Note:
If the T0CS bit is set to ‘1’, it will override
the TRIS function on the T0CKI pin.
REGISTER 4-3:
OPTION REGISTER (PIC12F508/509)
W-1
GPWU
GPPU
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
GPWU: Enable Wake-up on Pin Change bit (GP0, GP1, GP3)
1
= Disabled
0
= Enabled
bit 6
GPPU: Enable Weak Pull-ups bit (GP0, GP1, GP3)
1
= Disabled
0
= Enabled
bit 5
T0CS: Timer0 Clock Source Select bit
1
= Transition on T0CKI pin (overrides TRIS on the T0CKI pin)
0
= Transition on internal instruction cycle clock, FOSC/4
bit 4
T0SE: Timer0 Source Edge Select bit
1
= Increment on high-to-low transition on the T0CKI pin
0
= Increment on low-to-high transition on the T0CKI pin
bit 3
PSA: Prescaler Assignment bit
1
= Prescaler assigned to the WDT
0
= Prescaler assigned to Timer0
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