PIC16C55X(A)
4.2.2.1
STATUS REGISTER
It is recommended, therefore, that only BCF, BSF,
SWAPFand MOVWFinstructions be used to alter the STA-
TUS register because these instructions do not affect
any status bits. For other instructions, not affecting any
status bits, see the “Instruction Set Summary”.
The STATUS register, shown in Figure 4-6, 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
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 the
device logic. Furthermore, the TO and PD bits are not
writable. Therefore, the result of an instruction with the
STATUS register as the destination may be different
than intended.
Note 1: The IRP and RP1 bits (STATUS<7:6>)
are not used by the PIC16C55X(A) and
should be programmed as ’0'. 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.
For example, CLRF STATUSwill clear the upper-three
bits and set the Z bit. This leaves the status register as
000uu1uu(where u= unchanged).
FIGURE 4-6: STATUS REGISTER (ADDRESS 03H OR 83H)
Reserved Reserved R/W-0
IRP RP1 RP0
bit7
R-1
TO
R-1
PD
R/W-x
Z
R/W-x
DC
R/W-x
C
R
= Readable bit
W = Writable bit
- n = Value at POR reset
- x = Unknown at POR reset
bit0
bit 7:
IRP: Register Bank Select bit (used for indirect addressing)
1 = Bank 2, 3 (100h - 1FFh)
0 = Bank 0, 1 (00h - FFh)
The IRP bit is reserved on the PIC16C55X(A), always maintain this bit clear.
bit 6-5: RP1:RP0: Register Bank Select bits (used for direct addressing)
11= Bank 3 (180h - 1FFh)
10= Bank 2 (100h - 17Fh)
01= Bank 1 (80h - FFh)
00= Bank 0 (00h - 7Fh)
Each bank is 128 bytes. The RP1 bit is reserved on the PIC16C55X(A), always maintain this bit clear.
bit 4:
bit 3:
bit 2:
bit 1:
bit 0:
TO: Time-out bit
1 = After power-up, CLRWDTinstruction, or SLEEPinstruction
0 = A WDT time-out occurred
PD: Power-down bit
1 = After power-up or by the CLRWDTinstruction
0 = By execution of the SLEEPinstruction
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
DC: Digit carry/borrow bit (ADDWF, ADDLW,SUBLW,SUBWFinstructions)(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
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.
1997 Microchip Technology Inc.
Preliminary
DS40143B-page 17
MICROCHIP [ MICROCHIP ]
