PIC16F84A
2.2.2.1
STATUS REGISTER
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.
The STATUS register contains the arithmetic status of
the ALU, the RESET status and the bank select bit for
data memory.
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.
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
register as destination may be different than intended.
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 000u u1uu(where u= unchanged).
Note 3: When 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. The specified bit(s)
will be updated according to device logic
FIGURE 2-1: STATUS REGISTER (ADDRESS 03h, 83h)
R/W-0
IRP
R/W-0
RP1
R/W-0
RP0
R-1
TO
R-1
PD
R/W-x
Z
R/W-x
DC
R/W-x
C
R = Readable bit
W = Writable bit
bit7
bit0
U = Unimplemented bit,
read as ‘0’
- n = Value at POR reset
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:
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 (for ADDWFand ADDLWinstructions) (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 (for ADDWFand ADDLWinstructions)
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.
DS35007A-page 8
Preliminary
1998 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
