PIC18F6525/6621/8525/8621
It is recommended that only BCF, BSF, SWAPF, MOVFF
4.13 STATUS Register
and MOVWFinstructions are used to alter the STATUS
register, because these instructions do not affect the Z,
C, DC, OV or N bits in the STATUS register.
The STATUS register, shown in Register 4-3, contains
the arithmetic status of the ALU. As with any other SFR,
it can be the operand for any instruction.
For other instructions that do not affect Status bits, see
the instruction set summaries in Table 25-2.
If the STATUS register is the destination for an instruc-
tion that affects the Z, DC, C, OV or N bits, the results of
the instruction are not written; instead, the status is
updated according to the instruction performed. There-
fore, the result of an instruction with the STATUS register
as its destination may be different than intended. As an
example, CLRFSTATUSwill set the Z bit and leave the
remaining Status bits unchanged (‘000u u1uu’).
Note:
The C and DC bits operate as the borrow
and digit borrow bits respectively in
subtraction.
REGISTER 4-3:
STATUS REGISTER
U-0
—
U-0
—
U-0
—
R/W-x
R/W-x
OV
R/W-x
Z
R/W-x
DC
R/W-x
C
N
bit 7
bit 0
bit 7-5
bit 4
Unimplemented: Read as ‘0’
N: Negative bit
This bit is used for signed arithmetic (2’s complement). It indicates whether the result was
negative (ALU MSB = 1).
1= Result was negative
0= Result was positive
bit 3
OV: Overflow bit
This bit is used for signed arithmetic (2’s complement). It indicates an overflow of the
7-bit magnitude which causes the sign bit (bit 7) to change state.
1= Overflow occurred for signed arithmetic (in this arithmetic operation)
0= No overflow occurred
bit 2
bit 1
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
DC: Digit Carry/Borrow bit
For ADDWF, ADDLW, SUBLWand SUBWFinstructions:
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
Note:
For borrow, the polarity is reversed. A subtraction is executed by adding the
2’s complement of the second operand. For rotate (RRF, RLF) instructions, this bit
is loaded with either bit 4 or bit 3 of the source register.
bit 0
C: Carry/Borrow bit
For ADDWF, ADDLW, SUBLWand SUBWFinstructions:
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:
For borrow, the polarity is reversed. A subtraction is executed by adding the
2’s complement of the second operand. For rotate (RRF, RLF) instructions, this bit
is loaded with either the high- or low-order bit of the source register.
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
DS39612B-page 58
2005 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
