The outputs of registers R0, R1, R2, and R3 are connected through 4-to-1 multiplexers to the inputs of a fifth register, R4. Each register is 8 bits long. The required transfers, as dictated by four control variables, are Co = R4 ← Ro
C1= R4 ← R1
C2= R4 ← R2
C3= R4 ← R3

The control variables are mutually exclusive (i. e., only one variable can be equal to 1 at any time) while the other three are equal to 0. Also, no transfer into R4 is to occur for all control variables equal to 0.

a. Using registers and a multiplexer, draw a detailed logic diagram of the hardware that implements a single bit of these register transfers.
b. Draw a logic diagram of the simple logic that maps the control variables as inputs to three outputs: the two select variables for the multiplexer and the load signal for the register R4.