DM163006 Datasheet, PDF (61/320 Pages) Microchip Technology – High-Performance ROM-less Microcontrollers

PIC18C601/801
4.13 STATUS Register
The STATUS register, shown in Register 4-3, contains
the arithmetic status of the ALU. 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, C, OV, or N bits,
then the write to these five bits is disabled. These bits
are set or cleared according to the device logic. There-
fore, the result of an instruction with the STATUS regis-
ter as destination may be different than intended.
REGISTER 4-3: STATUS REGISTER
U-0
U-0
U-0
—
—
—
bit 7
For example, CLRF STATUS will clear all implemented
bits and set the Z bit. This leaves the STATUS register
as ---0 0100 (where - = unimplemented).
It is recommended, therefore, that only BCF, BSF,
SWAPF, MOVFF and MOVWF instructions are used to
alter the STATUS register, because these instructions
do not affect the Z, C, DC, OV, or N bits from the
STATUS register. For other instructions which do not
affect the status bits, see Table 20-2.
Note: The C and DC bits operate as a borrow and
digit borrow bit respectively, in subtraction.
R/W-x
N
R/W-x
OV
R/W-x
Z
R/W-x
DC
R/W-x
C
bit 0
bit 7-5
bit 4
bit 3
bit 2
bit 1
bit 0
Unimplemented: Read as '0'
N: Negative bit
This bit is used for signed arithmetic (2’s complement). It indicates whether the result of the ALU
operation was negative (ALU MSb = 1).
1 = Result was negative
0 = Result was positive
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
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 arithmetic addition and subtraction instructions
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 two’s
complement of the second operand. For rotate (RRCF, RRNCF, RLCF, and
RLNCF) instructions, this bit is loaded with either the bit 4, or bit 3 of the source
register.
C: Carry/borrow bit
For arithmetic addition and subtraction instructions
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 two’s
complement of the second operand. For rotate (RRCF, RLCF) 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
 2001 Microchip Technology Inc.
Advance Information
DS39541A-page 61