Once the MBR has the instruction from memory, it must be copied into the IR register. This is done by setting A to 7, F to identity A, and C to 3. MA must be set to 0 to "turn off" the memory. Why is it necessary to actually have a separate IR register, you might ask why not just use the value in the MBR? Remember that the instruction must be decoded so that a specific instruction wire will get set to 1 in order to direct the rest of the control operations. Since the MBR will later be used to fetch the operand and store the result, that specific instruction wire must not change during these micro-operations. Hence, there needs to be a stable and safe place for the instruction to reside.