PIC16F84A datasheet(8/68 Pages) MICROCHIP

8 / 68 page

PIC16F84A

DS35007A-page 8

Preliminary

2.2.2.1

STATUS REGISTER

The STATUS register contains the arithmetic status of

the ALU, the RESET status and the bank select bit for

data memory.

As with any register, the STATUS register can be the

destination for any instruction. If the STATUS register is

the destination for an instruction that affects the Z, DC

or C bits, then the write to these three bits is disabled.

These bits are set or cleared according to device logic.

Furthermore, the TO and PD bits are not writable.

Therefore, 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).

Only the BCF, BSF, SWAPF and MOVWF instructions

should be used to alter the STATUS register (Table 7-2)

because these instructions do not affect any status bit.

FIGURE 2-1:

STATUS REGISTER (ADDRESS 03h, 83h)

Note 1: The IRP and RP1 bits (STATUS<7:6>) are

not used by the PIC16F84A and should be

programmed as cleared. Use of these bits

as general purpose R/W bits is NOT

recommended, since this may affect

upward compatibility with future products.

Note 2: The C and DC bits operate as a borrow

and digit borrow out bit, respectively, in

subtraction. See the SUBLW and SUBWF

instructions for examples.

Note 3: When

the

STATUS

the

destination for an instruction that affects

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

three bits is disabled. The speciﬁed bit(s)

will be updated according to device logic

R/W-0

R-1

R/W-x

IRP

RP1

RP0

R = Readable bit

W = Writable bit

U = Unimplemented bit,

read as ‘0’

- n = Value at POR reset

bit7

bit0

bit 7:

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

The IRP bit is not used by the PIC16F84A. IRP should be maintained clear.

bit 6-5: RP1:RP0: Register Bank Select bits (used for direct addressing)

00 = Bank 0 (00h - 7Fh)

01 = Bank 1 (80h - FFh)

Each bank is 128 bytes. Only bit RP0 is used by the PIC16F84A. RP1 should be maintained clear.

bit 4:

TO: Time-out bit

1 = After power-up, CLRWDT instruction, or SLEEP instruction

0 = A WDT time-out occurred

bit 3:

PD: Power-down bit

1 = After power-up or by the CLRWDT instruction

0 = By execution of the SLEEP instruction

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 (for ADDWF and ADDLW instructions) (For borrow the polarity is reversed)

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

bit 0:

C: Carry/borrow bit (for ADDWF and ADDLW 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 (RRF, RLF) instructions, this bit is loaded with either the high or low

order bit of the source register.

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