Dmux

Dmux: 1x2

module demux1x2(y,s,i);
    output [1:0] y;
    input s;
    input i;

assign y[0] = (~s) & i;
assign y[1] = s & i;

endmodule

Dmux: 1x4:

module demux1x4(y,i,s);

    output [3:0] y;

    input i;

    input [1:0] s;

assign y[0] = (~s[1] & ~ s[0] & i);

assign y[1] = (~s[1] & s[0] & i);

assign y[2] = (s[1] & ~s[0] & i);

assign y[3] = (s[1] & s[0] & i);

endmodule