题解 | #4bit超前进位加法器电路#

`timescale 1ns/1ns

module lca_4(
	input		[3:0]       A_in  ,
	input	    [3:0]		B_in  ,
    input                   C_1   ,
 
 	output	 wire			CO    ,
	output   wire [3:0]	    S
);

wire [3:0] g;//生成进位项
wire [3:0] p;//传播进位项
wire C3;
assign g = A_in & B_in;
assign p = A_in ^ B_in;

assign C3   = g[3] | (p[3]&(g[2] | (p[2]&(g[1] | (p[1]&(g[0] | (p[0]&C_1)))))));
assign S[0] = p[0] ^ C_1;
assign S[1] = p[1] ^ (g[0] | (p[0]&C_1));
assign S[2] = p[2] ^ (g[1] | (p[1]&(g[0] | (p[0]&C_1))));
assign S[3] = p[3] ^ (g[2] | (p[2]&(g[1] | (p[1]&(g[0] | (p[0]&C_1))))));
//assign C2 = g[2] | (p[2]&(g[1] | (p[1]&(g[0] | (p[0]&C_1)))));
//assign C1 = g[1] | (p[1]&(g[0] | (p[0]&C_1)));
//assign C0 = g[0] | (p[0]&C_1);
assign CO = C3;

endmodule

超前进位的特点就是深度浅，运行速度快。但是面积大，比较复杂。可以直接根据输入比特进行计算，不需要中间变量