4-bit Comparator

Question

Problem: 4-bit Comparator. Solve this hands-on electronics task on EWskills.

Accepted Answer

A. Dataflow

module maxmin4 (
    input  [3:0] a, b, c, d,
    output [3:0] max,
    output [3:0] min
);
    wire [3:0] max_ab = (a >= b) ? a : b;
    wire [3:0] min_ab = (a  <  b) ? a : b;

    wire [3:0] max_cd = (c >= d) ? c : d;
    wire [3:0] min_cd = (c  <  d) ? c : d;

    assign max = (max_ab >= max_cd) ? max_ab : max_cd;
    assign min = (min_ab  <  min_cd) ? min_ab : min_cd;
endmodule

B. Behavioral RTL

module maxmin4 (
    input  [3:0] a, b, c, d,
    output reg [3:0] max,
    output reg [3:0] min
);
    reg [3:0] max_ab, min_ab, max_cd, min_cd;
    always @* begin
        // AB pair
        max_ab = (a >= b) ? a : b;
        min_ab = (a  <  b) ? a : b;
        // CD pair
        max_cd = (c >= d) ? c : d;
        min_cd = (c  <  d) ? c : d;
        // Final
        max = (max_ab >= max_cd) ? max_ab : max_cd;
        min = (min_ab  <  min_cd) ? min_ab : min_cd;
    end
endmodule

💡Remember

For unsigned 4-bit values, >=/< are synthesizable and map to comparators/muxes.
Comparator trees scale well (log-depth). The above is two levels of compare/mux.

68. 4-bit Comparator