encoder 4:2

// This code implements the functionality of a 4:2 Encoder. Note that it is not a priority encoder. The code also contains the test bench to test the functionality of the encoder.

module enc_4to2 (c1,c0,a3,a2,a1,a0);
input a3,a2,a1,a0;
output reg c1,c0;
always @ (*)
case ({a3,a2,a1,a0})
4'b0001:begin c1=1'b0;c0=1'b0;end
4'b0010:begin c1=1'b0;c0=1'b1;end
4'b0100:begin c1=1'b1;c0=1'b0;end
4'b1000:begin c1=1'b1;c0=1'b1;end
default:begin c1=1'bx;c0=1'bx;end
endcase
endmodule

module stimulus;
reg a3,a2,a1,a0;
wire c1,c0;
enc_4to2 e(c1,c0,a3,a2,a1,a0);
initial 
begin
$monitor($time, " c1 = %b , c0 = %b , a3 = %b , a2 = %b , a1 = %b , a0 = %b ",c1,c0,a3,a2,a1,a0);
#10 a3=1'b0;a2=1'b0;a1=1'b0;a0=1'b0;
#10 a3=1'b0;a2=1'b0;a1=1'b0;a0=1'b1;
#10 a3=1'b0;a2=1'b0;a1=1'b1;a0=1'b0;
#10 a3=1'b0;a2=1'b1;a1=1'b0;a0=1'b0;
#10 a3=1'b1;a2=1'b0;a1=1'b0;a0=1'b0;
#10 a3=1'b1;a2=1'b0;a1=1'b0;a0=1'b1;
#10 a3=1'b0;a2=1'b1;a1=1'b1;a0=1'b0;
#10 a3=1'b1;a2=1'b1;a1=1'b1;a0=1'b1;
end
endmodule