实验5-3：74LS138设计3：8译码器（行为描述）

`timescale 1ns / 1ps
//////////////////////////////////////////////////////////////////////////////////
// Company: 
// Engineer: 
// 
// Create Date:    15:41:01 11/15/2018 
// Design Name: 
// Module Name:    Trial_53 
// Project Name: 
// Target Devices: 
// Tool versions: 
// Description: 
//
// Dependencies: 
//
// Revision: 
// Revision 0.01 - File Created
// Additional Comments: 
//
//////////////////////////////////////////////////////////////////////////////////
module Trial_53(
    A,B,C,Y,G1,G2A,G2B
    );
     input wire A,B,C;
     input wire G1,G2A,G2B;
     output reg [7:0] Y;
     
     always @(*)
        begin
            Y=8'b11111111;
            if (G1&(~G2A)&(~G2B))
                begin
                    if((~A)&(~B)&(~C))     Y[0]=0;
                    else if((~A)&(~B)&(C)) Y[1]=0;
                    else if((~A)&(B)&(~C)) Y[2]=0;
                    else if((~A)&(B)&(C))  Y[3]=0;
                    else if((A)&(~B)&(~C)) Y[4]=0;
                    else if((A)&(~B)&(C))  Y[5]=0;
                    else if((A)&(B)&(~C))  Y[6]=0;
                    else if((A)&(B)&(C))   Y[7]=0;
                end
        end
endmodule

管脚约束文件

NET "G1"  IOSTANDARD = LVCMOS18;
NET "G2A" IOSTANDARD = LVCMOS18;
NET "G2B" IOSTANDARD = LVCMOS18;
NET "C"   IOSTANDARD = LVCMOS18;
NET "B"   IOSTANDARD = LVCMOS18;
NET "A"   IOSTANDARD = LVCMOS18;

NET "A"   LOC = W4;
NET "B"   LOC = V4;
NET "C"   LOC = V3;
NET "G1"  LOC = T3;
NET "G2A" LOC = U3;
NET "G2B" LOC = T4;


NET "Y[7]" IOSTANDARD = LVCMOS18;
NET "Y[6]" IOSTANDARD = LVCMOS18;
NET "Y[5]" IOSTANDARD = LVCMOS18;
NET "Y[4]" IOSTANDARD = LVCMOS18;
NET "Y[3]" IOSTANDARD = LVCMOS18;
NET "Y[2]" IOSTANDARD = LVCMOS18;
NET "Y[1]" IOSTANDARD = LVCMOS18;
NET "Y[0]" IOSTANDARD = LVCMOS18;

NET "Y[7]" LOC = R1;
NET "Y[6]" LOC = P2;
NET "Y[5]" LOC = P1;
NET "Y[4]" LOC = N2;
NET "Y[3]" LOC = M1;
NET "Y[2]" LOC = M2;
NET "Y[1]" LOC = L1;
NET "Y[0]" LOC = J2;


NET "G1"  PULLDOWN;
NET "G2A" PULLDOWN;
NET "G2B" PULLDOWN;
NET "C"   PULLDOWN;
NET "B"   PULLDOWN;
NET "A"   PULLDOWN;