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Bitwise logical AND stores in a bit ....

Arnaud DELEULE

Hi,

I get a curious result when compiling such a following code :

typedef union  {

  unsigned char                cCtrlFullByte;

  struct {
    unsigned char  bEnable          : 1;
    unsigned char  cUnused          : 7;

  }  cCtrlStruct;
} CtrlUnion;

void main (void)  {

    unsigned char  dummy = 0x55;
    CtrlUnion  xdata    bitUnion;

    bitUnion.cCtrlStruct.bEnable = dummy & 0x40;

    return;
}

It results in :
MOV A,#0x55
ANL A,#0x00
MOV R7,A
MOV DPTR, #0x0000
MOVX A,@DPTR
ANL A,#0xFE
ORL A,R7
MOVX @DPTR, A

I thought that the bit result of bitwise logical AND is 1 if result is not 0, else 0.
It seems that I didn't understand ANSI the same way than Keil compiler ? Am I wrong ?

Arnaud DELEULE

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  • 0 in reply to Arnaud DELEULE

    The code in Araund's example is correct. The first example where C is set from E0.6 (actually Accumulator bit 6 .. E0 is the ACC sfr) is exactly the value specified.

    In the second example, the and with 0x44 and add 0xff sets carry if either of the two bits in the mask are non-zero.

    Looks to me like the compiler did exactly as it should.

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  • 0 in reply to Arnaud DELEULE

    The code in Araund's example is correct. The first example where C is set from E0.6 (actually Accumulator bit 6 .. E0 is the ACC sfr) is exactly the value specified.

    In the second example, the and with 0x44 and add 0xff sets carry if either of the two bits in the mask are non-zero.

    Looks to me like the compiler did exactly as it should.

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