mahmood Elnasser wrote:
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If it was a pic then only 2 instructions are needed:

MOVWF R0;
SWAPF R0,f;

Sorry Mahmood, this is wrong.

The M.Karas's task is to exchange the low nibble of the accumulator (W in your case) and the high nibble of ram pointed by r0 register (lets say R0 in your case) without changing any other nibbles.

Regards,
George