串行移位寄存器原理与结构分析

1 串转并功能，通过移位寄存器和输出锁存器实现

2 FPGA需要通过74HC595这个芯片把16位的数据（sel+seg）变为并行端口用来驱动数码管

3 3.3V供电情况下，取SHCP时钟频率位12.5MHz（50-20ns,25-40ns,12.5-80ns），让其每40ns翻转一次，也就是每两个CLK周期翻转一次

上图所对应的代码段

	parameter CNT_MAX = 2;

	reg [7:0]divider_cnt;
	always@(posedge Clk or negedge Rst_n)
	if(!Rst_n)
		divider_cnt <= 0;
	else if(divider_cnt == CNT_MAX - 1'b1)
		divider_cnt <= 0;
	else
		divider_cnt <= divider_cnt + 1'b1;
		
	assign sck_plus = (divider_cnt == CNT_MAX - 1'b1)

	always@(posedge Clk or negedge Rst_n)
	if(!Rst_n)
		SH_CP <= 0;
	else if(sck_plus)
		SH_CP <= ~ SH_CP;

上图所对应打代码

	reg [7:0]divider_cnt;
	always@(posedge Clk or negedge Rst_n)
	if(!Rst_n)
		divider_cnt <= 0;
	else if(divider_cnt == 3)
		divider_cnt <= 0;
	else
		divider_cnt <= divider_cnt + 1'b1;
		
	assign sck_plus = (divider_cnt == 3)

	always@(posedge Clk or negedge Rst_n)
	if(!Rst_n)
		SH_CP <= 0;
	else if(sck_plus)
		SH_CP <= ~ SH_CP;

 32个时刻输出16位数据

	reg [5:0]SHCP_EDGE_CNT;//计的是SHCP的边沿变化
	
	always@(posedge Clk or negedge Rst_n)
	if(!Rst_n)
		SHCP_EDGE_CNT <= 0;
	else if(sck_plus)begin
		if(SHCP_EDGE_CNT == 32)
			SHCP_EDGE_CNT <= 0;
		else
			SHCP_EDGE_CNT <= SHCP_EDGE_CNT + 1'b1;
	end
	else
		SHCP_EDGE_CNT <= SHCP_EDGE_CNT;
		
	//根据SHCP_EDGE_CNT值是多少，决定干什么事
	always@(posedge Clk or negedge Rst_n)
	if(!Rst_n)begin
		ST_CP <= 1'b0;
		DS <= 1'b0;
		SH_CP <= 1'b0;
	end
	else begin
		case(SHCP_EDGE_CNT)
			0:begin SH_CP <= 0; ST_CP <= 1'd0; DS <= r_data[15];end
			1:begin SH_CP <= 1; ST_CP <= 1'd0;end
			2:begin SH_CP <= 0; DS <= r_data[14];end
			3:begin SH_CP <= 1; end
			4:begin SH_CP <= 0; DS <= r_data[13];end
			5:begin SH_CP <= 1; end
			6:begin SH_CP <= 0; DS <= r_data[12];end
			7:begin SH_CP <= 1; end
			8:begin SH_CP <= 0; DS <= r_data[11];end
			9:begin SH_CP <= 1; end
			10:begin SH_CP <= 0; DS <= r_data[10];end
			11:begin SH_CP <= 1; end
			12:begin SH_CP <= 0; DS <= r_data[9];end
			13:begin SH_CP <= 1; end
			14:begin SH_CP <= 0; DS <= r_data[8];end
			15:begin SH_CP <= 1; end
			16:begin SH_CP <= 0; DS <= r_data[7];end
			17:begin SH_CP <= 1; end
			18:begin SH_CP <= 0; DS <= r_data[6];end
			19:begin SH_CP <= 1; end
			20:begin SH_CP <= 0; DS <= r_data[5];end
			21:begin SH_CP <= 1; end
			22:begin SH_CP <= 0; DS <= r_data[4];end
			23:begin SH_CP <= 1; end
			24:begin SH_CP <= 0; DS <= r_data[3];end
			25:begin SH_CP <= 1; end
			26:begin SH_CP <= 0; DS <= r_data[2];end
			27:begin SH_CP <= 1; end
			28:begin SH_CP <= 0; DS <= r_data[1];end
			29:begin SH_CP <= 1; end
			30:begin SH_CP <= 0; DS <= r_data[0];end
			31:begin SH_CP <= 1; end
			32:begin ST_CP <= 1; end
			default:
				begin
					ST_CP <= 1'b0;
					DS <= 1'b0;
					SH_CP <= 1'b0;
				end
		endcase
	end

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