Datasheet

PIC18F46J11 FAMILY
DS39932D-page 96  2011 Microchip Technology Inc.
6.3.5 STATUS REGISTER
The STATUS register in Register 6-2, contains the
arithmetic status of the ALU. The STATUS register can
be the operand 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. Therefore, the result of an instruction with the
STATUS register as destination may be different than
intended. For example, CLRF STATUS will set the Z bit
but leave the other bits unchanged. The STATUS
register then reads back as ‘000u u1uu’. It is recom-
mended, 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 in the STATUS register.
For other instructions not affecting any Status bits, see
the instruction set summary in Table 27-2 and
Table 27-3.
Note: The C and DC bits operate as a borrow
and digit borrow bits respectively, in
subtraction.
REGISTER 6-2: STATUS REGISTER (ACCESS FD8h)
U-0 U-0 U-0 R/W-x R/W-x R/W-x R/W-x R/W-x
— — —NOVZDC
(1)
C
(2)
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 7-5 Unimplemented: Read as ‘0’
bit 4 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 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
(1)
For ADDWF, ADDLW, SUBLW and SUBWF instructions:
1 = A carry-out from the 4
th
low-order bit of the result occurred
0 = No carry-out from the 4
th
low-order bit of the result
bit 0 C: Carry/borrow
bit
(1)
For ADDWF, ADDLW, SUBLW and SUBWF instructions:
1 = A carry-out from the MSb of the result occurred
0 = No carry-out from the MSb of the result occurred
Note 1: For borrow,
the polarity is reversed. A subtraction is executed by adding the 2’s complement of the second
operand.