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Newbie dumb question

Stephen Magoon

Why, when I use the Simulator on this code, does A return as 0 when it should be 3?

MAIN:
        NOP
        MOV     DPTR, #CommandTable
        MOVX    A, @DPTR                ; Get the offset
        MOV     DPTR, #Subroutines
        JMP     @A+DPTR

CommandTable:
        DB Low(GetStatus - Subroutines)

Subroutines:
SetStatus:
        NOP
        NOP
        RET
GetStatus:
        NOP
        NOP
        RET

END

Thanks for your help.

Steve

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  • 0 in reply to ImPer Westermark

    The MOVX is accessing XDATA space, not CODE.

    E.g. the SILabs chips can be (via a SFR) be set to MOVX access code space, for flash writing purposes.

    Also, I have, when it was advatageous to the application, on occasion 'rewired' the '51 to be a VonNeuman machine.

    I doubt very much that this is what the OP is strugglinhg with, but the statement "MOVX is accessing XDATA space, not CODE" is not correct in SOME cases.

    Erik

Reply
  • 0 in reply to ImPer Westermark

    The MOVX is accessing XDATA space, not CODE.

    E.g. the SILabs chips can be (via a SFR) be set to MOVX access code space, for flash writing purposes.

    Also, I have, when it was advatageous to the application, on occasion 'rewired' the '51 to be a VonNeuman machine.

    I doubt very much that this is what the OP is strugglinhg with, but the statement "MOVX is accessing XDATA space, not CODE" is not correct in SOME cases.

    Erik

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