PIC16F87 datasheet(17/230 Pages) MICROCHIP

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DS30487D-page 17

PIC16F87/88

2.2.2.1

STATUS Register

The STATUS register, shown in Register 2-1, contains

the arithmetic status of the ALU, the Reset status and

the bank select bits for data memory.

The STATUS register can be the destination for any

instruction, as with any other register. If the STATUS

the Z, DC or C bits, then the write to these three bits is

disabled. These bits are set or cleared according to the

device logic. Furthermore, the TO and PD bits are not

writable. Therefore, the result of an instruction with the

STATUS register as destination may be different than

intended.

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

and MOVWF instructions are used to alter the STATUS

or DC bits from the STATUS register. For other

instructions

not

affecting

any

Status

bits,

see

Section 16.0 “Instruction Set Summary”.

STATUS: ARITHMETIC STATUS REGISTER (ADDRESS 03h, 83h, 103h, 183h)

Note:

The C and DC bits operate as a borrow

and digit borrow bit, respectively, in

subtraction. See the SUBLW and SUBWF

instructions for examples.

R/W-0

R-1

R/W-x

IRP

RP1

RP0

ZDC

bit 7

bit 0

bit 7

IRP: Register Bank Select bit (used for indirect addressing)

= Bank 2, 3 (100h-1FFh)

= Bank 0, 1 (00h-FFh)

bit 6-5

RP<1:0>: Register Bank Select bits (used for direct addressing)

= Bank 3 (180h-1FFh)

= Bank 2 (100h-17Fh)

= Bank 1 (80h-FFh)

= Bank 0 (00h-7Fh)

Each bank is 128 bytes.

bit 4

TO: Time-out bit

= After power-up, CLRWDT instruction or SLEEP instruction

= A WDT time-out occurred

bit 3

PD: Power-Down bit

= After power-up or by the CLRWDT instruction

= By execution of the SLEEP instruction

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 (ADDWF, ADDLW, SUBLW and SUBWF instructions)(1)

= 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 (ADDWF, ADDLW, SUBLW and SUBWF instructions)(1,2)

= 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 two’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

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

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