The number of registers are 4
Each register is of 8-bits
Common bus transfers 8-bits at a time.
Assuming four registers are
And eight bits of each register are defined as
1) a7, a6, ..., a0
2) b7, b6, ..., b0
3) c7, c6, ..., c0
4) d7, d6, ..., d0
Eight 4:1 Muxes are required to design this system,
4:1 MUX since there are 4 registers.
Eight MUXes since each register is of 8-bits
All the LSB's are connected as inputs to one of the 4:1 MUXes
Similarly, all bit 1's of each register is connected to one MUX
Finally, all MSB's are connected to the final 4:1 MUX
Two selection lines S1 and S0 are used to select the register and transfer them to the 8-bit bus