27.数码管的驱动，使用74HC595移位寄存器芯片

PS：升腾A7pro系列FPGA没有数码管外设，因此以AC620FPGA为例展开实验。

（1）共阳极数码管和共阴极数码管示意图：

• AC620中的数码管属于共阳极数码管，段选端口(dp,g,f,e,d,c,b,a)低电平即可点亮led。
• 人眼的视觉停留效应：当led以小于20ms的时间间隔进行闪烁时，在人眼看来，就是一直亮着的。
• 预使8个数码管实现动态扫描的效果，需要扫描间隔小于20ms/8 =2.5ms，不妨取1ms。
• 第一毫秒位选sel[0]高电平，其余sel[0:6]低电平；第二毫秒位选sel[1]高电平，其余sel[0]、sel[2:6]低电平，依次循环。

（2）段选、位选Verilog代码：

module hex(clk,reset_n,data,sel,seg);input clk;
input reset_n;
input [31:0]data;output reg[7:0]sel;
output reg[7:0]seg;//1ms = 1_000_000ns = 20ns * 50_000;
reg [15:0]cnt;
reg [2:0]sel_cnt;
reg [3:0]temp_data;
reg [7:0]r_sel;parameter MCNT = 49_999;//1ms计数器模块
always@(posedge clk or negedge reset_n)if(!reset_n)cnt <= 16'd0;else if(cnt == MCNT)cnt <= 16'd0;else cnt <= cnt + 16'd1;//sel_cnt计数器模块设计
always@(posedge clk or negedge reset_n)if(!reset_n)sel_cnt <= 3'd0;else if(cnt == MCNT)sel_cnt <= sel_cnt + 3'd1;else sel_cnt <= sel_cnt;//r_sel信号设计
always@(posedge clk or negedge reset_n)if(!reset_n)r_sel <= 8'h01;else begincase(sel_cnt)3'd0: r_sel <= 8'h01;3'd1: r_sel <= 8'h02;3'd2: r_sel <= 8'h04;3'd3: r_sel <= 8'h08;3'd4: r_sel <= 8'h10;3'd5: r_sel <= 8'h20;3'd6: r_sel <= 8'h40;3'd7: r_sel <= 8'h80;endcaseend//sel信号设计    打一拍的目的是为了和seg信号同步
always@(posedge clk)sel <= r_sel;//temp_data信号设计
always@(posedge clk or negedge reset_n)if(!reset_n)temp_data <= 4'd0;else begincase(sel_cnt)3'd0:temp_data <= data[3:0];3'd1:temp_data <= data[7:4];3'd2:temp_data <= data[11:8];3'd3:temp_data <= data[15:12];3'd4:temp_data <= data[19:16];3'd5:temp_data <= data[23:20];3'd6:temp_data <= data[27:24];3'd7:temp_data <= data[31:28];endcaseend//seg信号设计
always@(posedge clk or negedge reset_n)if(!reset_n)seg <= 8'hff;else begincase(temp_data)4'h0:seg <= 8'b1100_0000;4'h1:seg <= 8'b1111_1001;4'h2:seg <= 8'b1010_0100;4'h3:seg <= 8'b1011_0000;4'h4:seg <= 8'b1001_1001;4'h5:seg <= 8'b1001_0010;4'h6:seg <= 8'b1000_0010;4'h7:seg <= 8'b1111_1000;4'h8:seg <= 8'b1000_0000;4'h9:seg <= 8'b1001_0000;4'ha:seg <= 8'b1000_1000;4'hb:seg <= 8'b1000_0011;4'hc:seg <= 8'b1100_0110;4'hd:seg <= 8'b1010_0001;4'he:seg <= 8'b1000_0110;4'hf:seg <= 8'b1000_1110;endcaseendendmodule

（3）对应仿真文件代码：

`timescale 1ns/1nsmodule hex_tb;reg clk;reg reset_n;reg [31:0]data;wire [7:0]sel;wire [7:0]seg;hex hex_inst(.clk(clk),.reset_n(reset_n),.data(data),.sel(sel),.seg(seg));defparam hex_inst.MCNT = 499;initial clk = 1'd1;always #10 clk = ~clk;initial beginreset_n <= 1'd0;#25;reset_n <= 1'd1;#15;data <= 32'h00112233;#200_000;data <= 32'h44556677;#200_000;data <= 32'h8899aabb;#200_000;data <= 32'hccddeeff;#200_000;$stop;endendmodule

（4）仿真波形:

（5）74HC595芯片:

74HC595芯片内部工作原理：

• 先传段选，再传位选，先传高位，再传低位。(段位高低)
• 74HC595芯片在3.3v工作电压下，可以承受的工作频率为12.5MHz。

(6)74HC595驱动代码：

module hc595_driver(clk,reset_n,sel,seg,DIO,SCLK,RCLK);input clk;
input reset_n;
input [7:0]sel;
input [7:0]seg;output reg DIO;
output reg SCLK;
output reg RCLK;//74HC595芯片在3.3v工作电压下，可以承受的工作频率为12.5MHz，对应一个周期为80ns，半个周期为两个系统时钟周期
reg div_cnt;
reg [4:0]bit_cnt;//分频计数器设计
always@(posedge clk or negedge reset_n)if(!reset_n)div_cnt <= 1'd0;else div_cnt <= div_cnt + 1'd1;//bit_cnt设计
always@(posedge clk or negedge reset_n)if(!reset_n)bit_cnt <= 5'd0;else if(div_cnt == 1'd1)bit_cnt <= bit_cnt + 5'd1;else bit_cnt <= bit_cnt;//序列机设计
always@(posedge clk or negedge reset_n)if(!reset_n)beginDIO <= 1'd0;RCLK <= 1'd0;SCLK <= 1'd0;endelse if(div_cnt == 1'd1)begincase(bit_cnt)5'd0:	begin DIO <= seg[7];SCLK <= 1'd0;RCLK <= 1'd1;end5'd1:	begin SCLK <= 1'd1;RCLK <= 1'd0;end5'd2:	begin DIO <= seg[6];SCLK <= 1'd0;end5'd3:	begin SCLK <= 1'd1;end5'd4:	begin DIO <= seg[5];SCLK <= 1'd0;end5'd5:	begin SCLK <= 1'd1;end5'd6:	begin DIO <= seg[4];SCLK <= 1'd0;end5'd7:	begin SCLK <= 1'd1;end5'd8:	begin DIO <= seg[3];SCLK <= 1'd0;end5'd9:	begin SCLK <= 1'd1;end5'd10:begin DIO <= seg[2];SCLK <= 1'd0;end5'd11:begin SCLK <= 1'd1;end5'd12:begin DIO <= seg[1];SCLK <= 1'd0;end5'd13:begin SCLK <= 1'd1;end5'd14:begin DIO <= seg[0];SCLK <= 1'd0;end5'd15:begin SCLK <= 1'd1;end5'd16:begin DIO <= sel[7];SCLK <= 1'd0;end5'd17:begin SCLK <= 1'd1;end5'd18:begin DIO <= sel[6];SCLK <= 1'd0;end5'd19:begin SCLK <= 1'd1;end5'd20:begin DIO <= sel[5];SCLK <= 1'd0;end5'd21:begin SCLK <= 1'd1;end5'd22:begin DIO <= sel[4];SCLK <= 1'd0;end5'd23:begin SCLK <= 1'd1;end5'd24:begin DIO <= sel[3];SCLK <= 1'd0;end5'd25:begin SCLK <= 1'd1;end5'd26:begin DIO <= sel[2];SCLK <= 1'd0;end5'd27:begin SCLK <= 1'd1;end5'd28:begin DIO <= sel[1];SCLK <= 1'd0;end5'd29:begin SCLK <= 1'd1;end5'd30:begin DIO <= sel[0];SCLK <= 1'd0;end5'd31:begin SCLK <= 1'd1;endendcaseendelse beginDIO <= DIO;RCLK <= RCLK;SCLK <= SCLK;endendmodule

(7)顶层代码：

module hex_top(clk,reset_n,sw,DIO,SCLK,RCLK);input clk;input reset_n;input [3:0]sw;output DIO;output SCLK;output RCLK;reg [31:0]data;wire [7:0]sel;wire [7:0]seg;hex hex_inst(.clk(clk),.reset_n(reset_n),.data(data),.sel(sel),.seg(seg));hc595_driver hc595_driver_inst(.clk(clk),.reset_n(reset_n),.sel(sel),.seg(seg),.DIO(DIO),.SCLK(SCLK),.RCLK(RCLK));//data设计always@(posedge clk or negedge reset_n)if(!reset_n)data <= 32'd0;else begincase(sw)4'h1:data <= 32'h76543210;4'h2:data <= 32'hfedcba98;4'h4:data <= 32'h98765432;4'h8:data <= 32'h12345678;default:data <= 32'h00000000;endcaseendendmodule

（8）引脚绑定: