Microchip Technology AC244045 Data Sheet

DS41440C-page 24

 2010-2012 Microchip Technology Inc.

3.2.1.1

STATUS Register

The STATUS register, shown in 

, contains:

• the arithmetic status of the ALU
• the Reset status
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 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,
SWAPF and MOVWF instructions are used to alter the
STATUS register, because these instructions do not
affect any Status bits. For other instructions not
affecting any Status bits (Refer to 

             

Note 1: The C and DC bits operate as Borrow

and Digit Borrow out bits, respectively, in
subtraction.

U-0

U-0

U-0

R-1/q

R-1/q

R/W-0/u

R/W-0/u

R/W-0/u

—

—

—

TO

PD

Z

DC

C

bit 7

bit 0

Legend:
R = Readable bit

W = Writable bit

U = Unimplemented bit, read as ‘0’

u = Bit is unchanged

x = Bit is unknown

-n/n = Value at POR and BOR/Value at all other Resets

‘1’ = Bit is set

‘0’ = Bit is cleared

q = Value depends on condition

bit 7-5

Unimplemented: Read as ‘0’

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/Digit Borrow bit (ADDWF, ADDLW, SUBLW, SUBWF instructions)

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

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-order or low-order 
bit of the source register.