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2011-2015 Microchip Technology Inc.
DS40001609E-page 19
PIC16(L)F1508/9
3.3.1.1
STATUS Register
The STATUS register, shown in
, contains:
• the arithmetic status of the ALU
• the Reset status
The STATUS register can be the destination for any
instruction, like 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).
It is recommended, therefore, that only
BCF, BSF,
SWAPF
and
MOVWF
instructions are used to alter the
STATUS register, because these instructions do not
affect any Status bits. For other instructions not
affecting any Status bits (Refer to
28.0 “Instruction Set Summary”
Note 1:
The C and DC bits operate as Borrow
and Digit Borrow out bits, respectively, in
subtraction.
REGISTER 3-1:
STATUS: STATUS REGISTER
U-0
U-0
U-0
R-1/q
R-1/q
R/W-0/u
R/W-0/u
R/W-0/u
—
—
—
TO
PD
Z
DC
(1)
C
(1)
bit 7
bit 0
Legend:
R = Readable bit
W = Writable bit
U = Unimplemented bit, read as ‘0’
u = Bit is unchanged
x = Bit is unknown
-n/n = Value at POR and BOR/Value at all other Resets
‘1’ = Bit is set
‘0’ = Bit is cleared
q = Value depends on condition
bit 7-5
Unimplemented:
Read as ‘
0
’
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/Digit Borrow bit (
ADDWF
,
ADDLW
,
SUBLW
,
SUBWF
instructions)
(1)
1
= A carry-out from the 4th low-order bit of the result occurred
0
= No carry-out from the 4th low-order bit of the result
bit 0
C:
Carry/Borrow bit
(1)
(
ADDWF
,
ADDLW
,
SUBLW
,
SUBWF
instructions)
(1)
1
= A carry-out from the Most Significant bit of the result occurred
0
= No carry-out from the Most Significant bit of the result occurred
Note 1:
For Borrow, the polarity is reversed. A subtraction is executed by adding the two’s complement of the
second operand. For rotate (
RRF
,
RLF
) instructions, this bit is loaded with either the high-order or low-order
bit of the source register.
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