If you could assign function to the *reserved A5 instruction in the 8051, what would it be? My vote: Choice 1, movx dptr,@dptr+a Choise 2, dec dptr *From what I recall, this instruction is reserved for the interrupt mechanism, which (upon an interrupt) crams this instruction into the decoder as a special jump-to-vector command. Thus, its likely we'll never see any variant actually using the A5 instruction, but its fun to wish just the same.