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Thursday, February 17, 2011

microprocessor


                                                                      The Flags register 


          S-sign flag
        The sign flag is set if bit D7 of the accumulator is set after an arithmetic or logic operation.
          Z-zero flag
        Set if the result of the ALU operation is 0. Otherwise is reset. This flag is affected by operations on the accumulator as well as other registers. (DCR B).
          AC-Auxiliary Carry
        This flag is set when a carry is generated from bit D3 and passed to D4 . This flag is used only internally for BCD operations. (Section 10.5 describes BCD addition including the DAA instruction).
          P-Parity flag
        After an ALU operation if the result has an even # of 1’s the p-flag is set. Otherwise it is cleared. So, the flag can be used to indicate even parity.
          CY-carry flag
Discussed earlier

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