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Microcontroladores 8051

4.5.1. The PSW Program Status Word

PSW Program Status Word Register

The register PSW (Program Status Word) or the program status word contains information on the status of the CPU. Contains indicators or flags to use conditional statements to make decisions. These indicators are changed automatically when any of the instructions shown in the following table is executed, can also be modified by the user. The PSW is in direct address 0D0H (SFRs area) and the address bit support bit by bit.

Indicators or flags

  • C: Carry Flag.
  • AC: Auxiliary Carry Flag indicates the carry from bit 3, is used for BCD operations.
  • F0: User Indicator or general purpose.
  • Ov: overflow indicator, when a drift in the 6 th and 7 th bit at a time.
  • P: parity indicator indicates 1 when the number is odd about the Acc.
  • Rs 0 and Rs 1: Selection of bank records.

Rs1
RS0
Bank
Address
0 0 0 00H to 07H
0 1 1 08H to 0FH
1 0 2 10H 17H
1 1 3 18H to 1FH

Instructions affecting flags

Instruction
C
Ov
Ac
ADD x x x
ADDC x x x
SUBBED x x x
MUL 0 x
DIV 0 x
DA x
RRC x
RLC x
SETB C 1
CLR C 0
CPL C x
ANL C, bit x
ANL C, / bit x
ORL C, bit x
ORL C, / bit x
MOV C, bit x
CJNE x

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