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专栏前言

本专栏的内容主要是记录本人学习Verilog过程中的一些知识点，刷题网站用的是牛客网

分析

首先列出3-8译码器和全减器的真值表 全减器真值表如下

3-8译码器真值表如下

`timescale 1ns/1nsmodule decoder_38(input             E      ,input             A0     ,input             A1     ,input             A2     ,output reg       Y0n    ,  output reg       Y1n    , output reg       Y2n    , output reg       Y3n    , output reg       Y4n    , output reg       Y5n    , output reg       Y6n    , output reg       Y7n    
);always @(*)beginif(!E)beginY0n = 1'b1;Y1n = 1'b1;Y2n = 1'b1;Y3n = 1'b1;Y4n = 1'b1;Y5n = 1'b1;Y6n = 1'b1;Y7n = 1'b1;end  else begincase({A2,A1,A0})3'b000 : beginY0n = 1'b0; Y1n = 1'b1; Y2n = 1'b1; Y3n = 1'b1; Y4n = 1'b1; Y5n = 1'b1; Y6n = 1'b1; Y7n = 1'b1;end 3'b001 : beginY0n = 1'b1; Y1n = 1'b0; Y2n = 1'b1; Y3n = 1'b1; Y4n = 1'b1; Y5n = 1'b1; Y6n = 1'b1; Y7n = 1'b1;end 3'b010 : beginY0n = 1'b1; Y1n = 1'b1; Y2n = 1'b0; Y3n = 1'b1; Y4n = 1'b1; Y5n = 1'b1; Y6n = 1'b1; Y7n = 1'b1;end 3'b011 : beginY0n = 1'b1; Y1n = 1'b1; Y2n = 1'b1; Y3n = 1'b0; Y4n = 1'b1; Y5n = 1'b1; Y6n = 1'b1; Y7n = 1'b1;end 3'b100 : beginY0n = 1'b1; Y1n = 1'b1; Y2n = 1'b1; Y3n = 1'b1; Y4n = 1'b0; Y5n = 1'b1; Y6n = 1'b1; Y7n = 1'b1;end 3'b101 : beginY0n = 1'b1; Y1n = 1'b1; Y2n = 1'b1; Y3n = 1'b1; Y4n = 1'b1; Y5n = 1'b0; Y6n = 1'b1; Y7n = 1'b1;end 3'b110 : beginY0n = 1'b1; Y1n = 1'b1; Y2n = 1'b1; Y3n = 1'b1; Y4n = 1'b1; Y5n = 1'b1; Y6n = 1'b0; Y7n = 1'b1;end 3'b111 : beginY0n = 1'b1; Y1n = 1'b1; Y2n = 1'b1; Y3n = 1'b1; Y4n = 1'b1; Y5n = 1'b1; Y6n = 1'b1; Y7n = 1'b0;end default: beginY0n = 1'b1; Y1n = 1'b1; Y2n = 1'b1; Y3n = 1'b1; Y4n = 1'b1; Y5n = 1'b1; Y6n = 1'b1; Y7n = 1'b1;endendcase  end 
end    endmodulemodule decoder1(input             A     ,input             B     ,input             Ci    ,output wire       D     ,output wire       Co         
);wire [7:0] Y ; assign D = ~Y[1] + ~Y[2] + ~Y[4] + ~Y[7] ;assign Co = ~Y[1] + ~Y[2] + ~Y[3] + ~Y[7] ;decoder_38 d1(.E (1   ),.A0(Ci   ),.A1(B   ),.A2(A   ),.Y0n(Y[0]),.Y1n(Y[1]),.Y2n(Y[2]),.Y3n(Y[3]),.Y4n(Y[4]),.Y5n(Y[5]),.Y6n(Y[6]),.Y7n(Y[7]));endmodule