Structural Gate Level Description of Decoder

STRUCTURAL GATE LEVEL DESCRIPTION OF DECODER

1. DECODER

module mux (sel, res);

input  [2:0] sel;

output [7:0] res;

reg [7:0] res;

always @(sel or res)

begin

case (sel)

3’b000 : res = 8’b00000001;

3’b001 : res = 8’b00000010;

3’b010 : res = 8’b00000100;

3’b011 : res = 8’b00001000;

3’b100 : res = 8’b00010000;

3’b101 : res = 8’b00100000;

3’b110 : res = 8’b01000000;

default : res = 8’b10000000;

endcase

end

endmodule

2. EQUALITY DETECTOR

3. Comparator

module compar(a, b, cmp);

input [7:0] a;

input [7:0] b;

output cmp;

assign cmp = (a >= b) ? 1’b1 : 1’b0;

endmodule

4. Priority Encoder.

module priority (sel, code);

input  [7:0] sel;

output [2:0] code;

reg [2:0] code;

always @(sel)

begin

if (sel[0])

code = 3’b000;

else if (sel[1]) code = 3’b001;

else if (sel[2]) code = 3’b010;

else if (sel[3]) code = 3’b011;

else if (sel[4]) code = 3’b100;

else if (sel[5]) code = 3’b101;

else if (sel[6]) code = 3’b110;

else if (sel[7]) code = 3’b111;

else

code = 3’bxxx;

end

endmodule

5. HALF ADDER module ha(s,cy,a,b);

input a,b;

output s,cy;

assign s=(a ^ b);

assign cy=(a & b);

endmodule

6. FULL ADDER

Program:

library ieee;

use ieee.std_logic_1164.all;

entity full is

port(a,b,c:in std_logic;

sum, carry:out std_logic);

end full;

architecture behave of full is

begin

sum <= a xor b xor c;

carry <= (a and b) or (b and c) or (c and a);

end behave;

7. Ripple carry adder module adder(a, b, sum, co);

input [7:0] a; input [7:0] b; output [7:0] sum; output co; wire [8:0] tmp;

assign tmp = a + b; assign sum = tmp [7:0]; assign co = tmp [8];

endmodule

8. D-LATCH

9. D-FLIP FLOP

module dff(q,d,rst,clk); input d,rst,clk; output q;

reg q;

always@(posedge rst or negedge clk) if (rst)

q=1'b0; else q=d;

endmodule