标签:简单 scale out efault log default define esc case
在分频器电路中最重要的概念有两个;1)奇分频/偶分频;2)占空比。
A)其中最简单的就是二分频电路,占空比为50%,其Verilog程序为
1 module half_clk(clr,clk_in,clk_out,out2); 2 input clr,clk_in; 3 output clk_out,out2; 4 reg clk_out,out2; 5 6 always @(posedge clk_in) 7 begin 8 if (clr==0) begin clk_out=0; out2=1;end 9 else begin clk_out<=~clk_out; out2=~out2;end 10 end 11 endmodule
波形图如下所示:
B)采用计数器实现计数分频(偶数)占空比为50%,如实现40分频,程序如下:
1 module fdivision(rst,clkin,clkout); 2 input rst,clkin; 3 output clkout; 4 reg clkout; 5 reg [4:0]i; 6 always @(posedge clkin) 7 begin 8 if(!rst) begin clkout<=0; i<=0;end 9 else begin 10 if(i==19) 11 begin clkout<=~clkout;i<=0;end 12 else 13 i<=i+1; 14 end 15 end 16 endmodule
波形图:
C)采用相与/相或的方式实现奇分频,以及占空比可调分频器;如5分频,占空比分别为50%,40%
1 module fdivision5(clkin,clkout); 2 input clkin; 3 output clkout; 4 wire clkout; 5 reg [2:0]step,step1; 6 always @(posedge clkin) 7 begin 8 case(step) 9 3‘b000:step<=3‘b010; 10 3‘b010:step<=3‘b100; 11 3‘b100:step<=3‘b001; 12 3‘b001:step<=3‘b011; 13 3‘b011:step<=3‘b000; 14 default step<=3‘b000; 15 endcase 16 end 17 always @(negedge clkin) 18 begin 19 case(step1) 20 3‘b000:step1<=3‘b010; 21 3‘b010:step1<=3‘b100; 22 3‘b100:step1<=3‘b001; 23 3‘b001:step1<=3‘b011; 24 3‘b011:step1<=3‘b000; 25 default step1<=3‘b000; 26 endcase 27 end 28 assign clkout=(step[0]|step1[0]); 29 endmodule
顶层文件(testbench):
1 `timescale 1ns/1ns 2 `define half_period 20 3 module fdivision5_test; 4 reg clkin; 5 wire clkout; 6 wire step,step1; 7 initial 8 begin 9 clkin=0; 10 end 11 always #`half_period clkin=~clkin; 12 fdivision5 m(clkin,clkout); 13 assign step=m.step; 14 assign step1=m.step1; 15 endmodule
波形图:
Verilog学习笔记简单功能实现(六)...............计数分频电路
标签:简单 scale out efault log default define esc case
原文地址:http://www.cnblogs.com/SYoong/p/6044803.html