PIC12F508/509/16F505
DS41236E-page 22
2009 Microchip Technology Inc.
4.4
STATUS Register
This register contains the arithmetic status of the ALU,
the Reset status and the page preselect bit.
The STATUS register can be the destination for any
instruction, as with any other register. If the STATUS
register is the destination for an instruction that affects
the Z, DC or C bits, then the write to these three bits is
disabled. These bits are set or cleared according to the
device logic. Furthermore, the TO and PD bits are not
writable. Therefore, the result of an instruction with the
STATUS register as destination may be different than
intended.
For example, CLRF STATUS, will clear the upper three
bits and set the Z bit. This leaves the STATUS register
as 000u u1uu (where u = unchanged).
Therefore, it is recommended that only BCF, BSF and
MOVWF
instructions be used to alter the STATUS regis-
ter. These instructions do not affect the Z, DC or C bits
from the STATUS register. For other instructions which
REGISTER 4-1:
STATUS REGISTER (ADDRESS: 03h) (PIC12F508/509)
R/W-0
R-1
R/W-x
GPWUF
—PA0
TO
PD
ZDC
C
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
GPWUF: GPIO Reset bit
1
= Reset due to wake-up from Sleep on pin change
0
= After power-up or other Reset
bit 6
Reserved: Do not use
bit 5
PA0: Program Page Preselect bits(1)
1
= Page 1 (200h-3FFh)
0
= Page 0 (000h-1FFh)
Each page is 512 bytes.
Using the PA0 bit as a general purpose read/write bit in devices which do not use it for program page preselect is
not recommended, since this may affect upward compatibility with future products.
bit 4
TO: Time-Out bit
1
= After power-up, CLRWDT instruction, or SLEEP instruction
0
= A WDT time-out occurred
bit 3
PD: Power-Down bit
1
= After power-up or by the CLRWDT instruction
0
= By execution of the SLEEP instruction
bit 2
Z: Zero bit
1
= The result of an arithmetic or logic operation is zero
0
= The result of an arithmetic or logic operation is not zero
bit 1
DC: Digit Carry/Borrow bit (for ADDWF and SUBWF instructions)
ADDWF:
1
= A carry from the 4th low-order bit of the result occurred
0
= A carry from the 4th low-order bit of the result did not occur
SUBWF:
1
= A borrow from the 4th low-order bit of the result did not occur
0
= A borrow from the 4th low-order bit of the result occurred
bit 0
C: Carry/Borrow bit (for ADDWF, SUBWF and RRF, RLF instructions)
ADDWF:
SUBWF:
RRF
or RLF:
1
= A carry occurred
1
= A borrow did not occur
Load bit with LSb or MSb, respectively
0
= A carry did not occur
0
= A borrow occurred
Note
1:
This bit is used on the PIC12F509. For code compatibility do not use this bit on the PIC12F508.