PIC16C641 datasheet(21/136 Pages) MICROCHIP

21 / 136 page

Preliminary

DS30559A-page 21

PIC16C64X & PIC16C66X

4.2.2.1

STATUS REGISTER

The STATUS register, shown in Figure 4-5, 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, like 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 000uu1uu (where u = unchanged).

It is recommended, therefore, that only BCF, BSF,

SWAPF,

and MOVWF instructions are used to alter the

STATUS register because these instructions do not

affect any status bit. For other instructions, not affecting

any status bits, see the “Instruction Set Summary.”

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

reserved

the

PIC16C64X

PIC16C66X and should be maintained

clear. Use of these bits as general pur-

pose 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.

FIGURE 4-5:

STATUS REGISTER (ADDRESS 03h, 83h)

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)

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

0 = Bank 0, 1 (00h - FFh)

Bit IRP is reserved on the PIC16C64X & PIC16C66X, always maintain this bit clear.

bit 6-5: RP1:RP0: 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 RP1 is reserved on the PIC16C64X & PIC16C66X, always maintain this bit

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 (ADDWF, ADDLW,SUBLW,SUBWF 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 (ADDWF, ADDLW,SUBLW,SUBWF 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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