Like this?
ReverseByte:
   jz   RevByteX1
   movc a,@a+pc
RevByteX1:
   ret
   db   80h,40h,0C0h,20h,0A0h,60h
... etc.</i>

nope

but like this
ReverseByte:
   inc a
   movc a,@a+pc
   ret
   db   0,80h,40h,0C0h,20h,0A0h,60h,......