mov   r0,#Source
   mov   r1,#Destination     ;set up pointers
Loop:
   mov   a,@r0               ;pick a byte from source 
   inc   r0                  ;  and advance pointer
   mov   @r1,a               ;store the byte to destination
   inc   r1                  ;  and advance pointer
   cjne  r0,#Source+4,Loop   ;loop until end