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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.