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PIC18F2450/4450

DS39760A-page 66

Advance Information

2006 Microchip Technology Inc.

5.3.6

STATUS REGISTER

The STATUS register, shown in Register 5-2, contains

the arithmetic status of the ALU. As with any other SFR,

it can be the operand for any instruction.

If the STATUS register is the destination for an instruction

that affects the Z, DC, C, OV or N bits, the results of the

instruction are not written; instead, the STATUS register

is updated according to the instruction performed.

Therefore, the result of an instruction with the STATUS

As an example, CLRF STATUS will set the Z bit and leave

the remaining Status bits unchanged (‘000u u1uu’).

It is recommended that only BCF, BSF, SWAPF, MOVFF

and MOVWF instructions are used to alter the STATUS

C, DC, OV or N bits in the STATUS register.

For other instructions that do not affect Status bits, see

the instruction set summaries in Table 19-2 and

Table 19-3.

Note:

The C and DC bits operate as the Borrow

and Digit Borrow bits, respectively, in

subtraction.

REGISTER 5-2:

STATUS REGISTER

U-0

R/W-x

—

—N

DC(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).

= Result was negative

= 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 of the result) to change state.

= Overflow occurred for signed arithmetic (in this arithmetic operation)

= No overflow occurred

bit 2

Z: Zero bit

= The result of an arithmetic or logic operation is zero

= 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:

= A carry-out from the 4th low-order bit of the result occurred

= No carry-out from the 4th low-order bit of the result

bit 0

C: Carry/Borrow bit(2)

For ADDWF, ADDLW, SUBLW and SUBWF instructions:

= A carry-out from the Most Significant bit of the result occurred

= 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 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.

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.

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