P12C508 datasheet(14/84 Pages) MICROCHIP

14 / 84 page

PIC12C5XX

DS40139A-page 14

Advance Information

4.3

STATUS Register

This register contains the arithmetic status of the ALU,

the RESET status, and the page preselect bit for

program memories larger than 512 words.

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 and

MOVWF

instructions be used to alter the STATUS

DC or C bits from the STATUS register. For other

instructions, which do affect STATUS bits, see Table 8-

2, Instruction Set Summary.

FIGURE 4-4:

STATUS REGISTER (ADDRESS:03h)

R/W-0

R-1

R/W-x

GPWUF

—

PA0

R = Readable bit

W = Writable bit

- n = Value at POR reset

bit7

bit0

bit 7:

GPWUF: GPIO reset bit

1 = Reset from wake-up from SLEEP on pin change

0 = After power up or other reset

bit 6:

Unimplemented

bit 5:

PA0: Program page preselect bits

1 = Page 1 (200h - 3FFh) - PIC12C509

0 = Page 0 (000h - 1FFh) - PIC12C508 and PIC12C509

Each page is 512 bytes.

Using the PA0 bit as a general purpose read/write bit in devices which do not use it for program

page preselect is not recommended since this may affect upward compatibility with future products.

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 SUBWF instructions)

ADDWF

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

0 = A carry from the 4th low order bit of the result did not occur

SUBWF

1 = A borrow from the 4th low order bit of the result did not occur

0 = A borrow from the 4th low order bit of the result occurred

bit 0:

C: Carry/borrow bit (for ADDWF, SUBWF and RRF, RLF instructions)

ADDWF

SUBWF

RRF or RLF

1 = A carry occurred

1 = A borrow did not occur

Load bit with LSB or MSB, respectively

0 = A carry did not occur

0 = A borrow occurred

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