Microchip Technology PIC16C63A, Operator'S Manual

Page: 19 / 184

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2000 Microchip Technology Inc. DS30605C-page 19
PIC16C63A/65B/73B/74B
4.2.2.1 STATUS Register
The STATUS register, shown in Register 4-1, 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, as with any other register. If the STATUS reg-
ister 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 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 that only
BCF, BSF, SWAPF
and
MOVWF
instructions be used to alter the STATUS regis-
ter. These instructions do not affect the Z, C or DC bits
in the STATUS register. For other instructions which do
not affect status bits, see the "Instruction Set Sum-
mary."
REGISTER 4-1: STATUS REGISTER (ADDRESS 03h, 83h)
Note 1: These devices do not use bits IRP and
RP1 (STATUS<7:6>), maintain these bits
clear to ensure upward compatibility with
future products.
2: The C and DC bits operate as borrow and
digit borrow bits, respectively, in subtrac-
tion. See the
SUBLW
and
SUBWF
instruc-
tions for examples.
R/W-0 R/W-0 R/W-0 R-1 R-1 R/W-x R/W-x R/W-x
IRP
(1)
RP1
(1)
RP0 TO PD Z DC C
(2)
bit 7 bit 0
bit 7 IRP
(1)
: Register Bank Select bit (used for indirect addressing)
1
= Bank 2, 3 (100h - 1FFh)
0
= Bank 0, 1 (00h - FFh)
bit 6-5 RP1
(1)
: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
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
(2)
: 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 1: Maintain the IRP and RP1 bits clear.
2: For borrow and digit borrow, the polarity is reversed. A subtraction is executed by
adding the two’s complement of the second operand. For rotate (
RRF,RLF
) instruc-
tions, this bit is loaded with either the high or low order bit of the source register.
Legend:
R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’
-n = Value at POR ’1’ = Bit is set ’0’ = Bit is cleared x = Bit is unknown