Question

Draw the logic diagram of a four-bit register with four D flip-flops and four 4 X 1 multiplexers with mode selection inputs s₁ and s₀. The register operates according to he following function table and produces the output Y = {y₃, y₂, y₁, y₀}:

s0 s1 Register Operation
0 0 load the parallel data = {i₃, i₂, i₁, i₀}
0 1 clear the register to 0 (synchronous with the clock)
1 0 complete the 4-bit output
1 1 hold (no change)
assume the D flip-flops come with the clockk source, clk, and active-low reset signal, rst_n, as shown in the following. the 4x1 multiplexer is also listed for your reference.
a0→ 0
d → → q a1→ 1 MUX → Y
DFF a2→ 2
clk→ →q' a3→ 3
rst_n ↑ 2
{s₁, s₀}

Answer 1

The logic diagram requested by the student involves four D flip-flops and four 4x1 multiplexers managed by mode selection inputs s1 and s0 to perform load, clear, output, and hold operations of a four-bit register.

Step-by-step explanation:

The student is asking for a logic diagram of a four-bit register using D flip-flops and multiplexers. This digital circuit uses a control signal, comprised of s1 and s0, to determine its operation mode which includes: loading parallel data, clearing the register, outputting the current value, or holding its state.

In the design, four D flip-flops act as the storage elements for the register's bits, while the four 4x1 multiplexers control the input to the flip-flops based on the mode selection inputs. Each D flip-flop's D input is connected to its corresponding multiplexer's output. The multiplexer's inputs (a0, a1, a2, and a3) correspond to the various operations as per the function table, with 'i' being the input data for the load operation, '0' for the clear operation, and 'q'/'q'' for the output and hold operations respectively.

For the clear operation, all multiplexer inputs corresponding to '1' will be tied to logic '0'. Mode selection inputs are connected to each multiplexer to determine the desired function (load, clear, output, hold) that the register should perform upon the clock signal's rising edge.