Question

How many times the ‘RL’ instruction needs to be executed, in order to mimic the ‘SWAP’ instruction in an 8051 microcontroller?

Answer 1

The correct answer is - 4 times.

Many applications have a need to carry out a bitwise rotation of the operand. The 8051 microcontrollers also have rotation instructions like RR, RL, RRC, and RLC that have been specifically designed for this purpose. They give a program that allows left or right rotation of the accumulator.

A SWAP instruction has the higher and the lower nibble of a byte. Therefore, the RL command will have to be used 4 times. This will swap the higher nibble and the lower nibble exactly like it is for the SWAP instruction. However. using the using RL 4 times will take up 4 times more of the memory and the time.