PIC18LF4331 datasheet(74/392 Pages) MICROCHIP

74 / 392 page

PIC18F2331/2431/4331/4431

DS39616D-page 74

 2010 Microchip Technology Inc.

6.6

STATUS Register

The STATUS register, shown 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. There-

fore, the result of an instruction with the STATUS

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, 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

bits, see Table 24-2.

Note:

The C and DC bits operate as a Borrow

and Digit Borrow bit respectively, in

subtraction.

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

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) to change state.

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

= No overflow occurred

bit 2

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

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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