Andrew T Kelley wrote:
>
> Hi,
>
> I would like to know why xorlw has 255 for a limit while xorwf only has a
> 127 for a limit.
>
> Please tell me why.
>
> Thanks,
> Andrew K.
> ________________________________________________________________
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XORLW instruction

11 1010 kkkk kkkk

kkkk kkkk = 8 bits of literal data

Therefore the literal data can be 0 - 255 (8 bits)

xorlw 0xFF    11 1010 1111 1111
xorlw 0x09    11 1010 0000 1001

etc.


XORWF instruction

00 0110 dfff ffff

d = destination bit
0 = result to W Reg
1 = result back to file register specified in the instruction

fff ffff = 7 bits of RAM address data

Therefore the address data can be 0 - 127 (7 bits)

xorwf 0x0C    00 0110 1000 1100
xorwf 0x8C    00 0110 1000 1100   bit 8 is truncated
xorwf 0xFF,w  00 0110 0111 1111   bit 8 is truncated







--
Best regards

Tony

http://www.picnpoke.com
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