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case语句的用法：
计数器不断的计数，每一个num对应数码管一种数据的输出。实例通俗易懂，一目了然。
`timescale 1ns / 1ps// Company:
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// 欢迎加入EDN的FPGA/CPLD助学小组一起讨论：http://group.ednchina.com/1375/module led_seg7(clk,rst_n,sm_cs1_n,sm_cs2_n,sm_db );input clk; // 50MHz
input rst_n; // 复位信号，低有效output sm_cs1_n,sm_cs2_n; //数码管片选信号，低有效
output[6:0] sm_db; //7段数码管（不包括小数点）reg[24:0] cnt; //计数器，最大可以计数到2的25次方*20ns=640msalways @ (posedge clk or negedge rst_n)if(!rst_n) cnt <= 25'd0;else cnt <= cnt+1'b1; //循环计数reg[3:0] num; //显示数值always @ (posedge clk or negedge rst_n)if(!rst_n) num <= 4'd0;else if(cnt == 25'h1ffffff) num <= num+1'b1; //每640ms增一//-------------------------------------------------------------------------------
/* 共阴极 :不带小数点;0, 1, 2, 3, 4, 5, 6, 7, db 3fh,06h,5bh,4fh,66h,6dh,7dh,07h ;8, 9, a, b, c, d, e, f , 灭 db 7fh,6fh,77h,7ch,39h,5eh,79h,71h,00h*/
parameter seg0 = 7'h3f,seg1 = 7'h06,seg2 = 7'h5b,seg3 = 7'h4f,seg4 = 7'h66,seg5 = 7'h6d,seg6 = 7'h7d,seg7 = 7'h07,seg8 = 7'h7f,seg9 = 7'h6f,sega = 7'h77,segb = 7'h7c,segc = 7'h39,segd = 7'h5e,sege = 7'h79,segf = 7'h71;reg[6:0] sm_dbr; //7段数码管（不包括小数点）always @ (num)case (num) //NUM值显示在两个数码管上4'h0: sm_dbr <= seg0;4'h1: sm_dbr <= seg1;4'h2: sm_dbr <= seg2;4'h3: sm_dbr <= seg3;4'h4: sm_dbr <= seg4;4'h5: sm_dbr <= seg5;4'h6: sm_dbr <= seg6;4'h7: sm_dbr <= seg7;4'h8: sm_dbr <= seg8;4'h9: sm_dbr <= seg9;4'ha: sm_dbr <= sega;4'hb: sm_dbr <= segb;4'hc: sm_dbr <= segc;4'hd: sm_dbr <= segd;4'he: sm_dbr <= sege;4'hf: sm_dbr <= segf;default: ;endcaseassign sm_db = sm_dbr;
assign sm_cs1_n = 1'b0; //数码管1常开
assign sm_cs2_n = 1'b0; //数码管2常开endmodule
Enjoy it.