Spartan-6 FPGA 嵌入式套件试用（五）----- 串口接收

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Spartan-6 FPGA 嵌入式套件试用（五）----- 串口接收 [复制链接]

接着上一篇，这篇主要来学习一下串口的接收，设计的思路为：

1.       PC端用串口助手发送数据；

2.       Xilinx fpga同过串口接收数据；

3.       同过接收到的数据来控制板子上的LED的状态，数据和LED的对应关系如下：

 

 

对应的Bit为1 时，LED亮；为0时，LED灭。

 

串口异步接收部分的框图如下：

 

具体实现如下：

// RS-232 RX module

module async_receiver(clk, RxD, RxD_data_ready, RxD_data, RxD_endofpacket, RxD_idle);

input clk, RxD;

output RxD_data_ready; 

output [7:0] RxD_data;

 

parameter ClkFrequency = 27000000;    // Spartan-6板子上的27MHz时钟

parameter Baud = 115200;             //波特率设置115200

 

 

output RxD_endofpacket;  //一个时钟宽度，如果没有其他数据需要接收，RxD_idle等于1

output RxD_idle;         //没有新数据接收的指示

 

 

//产生波特率

parameter Baud8 = Baud*8;

parameter Baud8GeneratorAccWidth = 16;

wire [Baud8GeneratorAccWidth:0] Baud8GeneratorInc = ((Baud8<<(Baud8GeneratorAccWidth-7))+(ClkFrequency>>8))/(ClkFrequency>>7);

reg [Baud8GeneratorAccWidth:0] Baud8GeneratorAcc;

 

always @(posedge clk)

     Baud8GeneratorAcc <= Baud8GeneratorAcc[Baud8GeneratorAccWidth-1:0] + Baud8GeneratorInc;

 

wire Baud8Tick = Baud8GeneratorAcc[Baud8GeneratorAccWidth];

 

//同步RxD信号

reg [1:0] RxD_sync_inv;

always @(posedge clk)

             if(Baud8Tick) RxD_sync_inv <= {RxD_sync_inv[0], ~RxD};

 

reg [1:0] RxD_cnt_inv;

reg RxD_bit_inv;

 

//对开始信号Start进行检测

always @(posedge clk)

if(Baud8Tick)

begin

if( RxD_sync_inv[1] && RxD_cnt_inv!=2'b11) RxD_cnt_inv <= RxD_cnt_inv + 2'h1;

else

if(~RxD_sync_inv[1] && RxD_cnt_inv!=2'b00) RxD_cnt_inv <= RxD_cnt_inv - 2'h1;

 

if(RxD_cnt_inv==2'b00) RxD_bit_inv <= 1'b0;

else

if(RxD_cnt_inv==2'b11) RxD_bit_inv <= 1'b1;

end

 

reg [3:0] state;

reg [3:0] bit_spacing;

 

wire next_bit = (bit_spacing==4'd10);

 

always @(posedge clk)

if(state==0)

bit_spacing <= 4'b0000;

else

if(Baud8Tick)

bit_spacing <= {bit_spacing[2:0] + 4'b0001} | {bit_spacing[3], 3'b000};

 

//一旦检测到"开始位"，使用如下的状态机可以检测出接收到每一位数据

always @(posedge clk)

if(Baud8Tick)

case(state)

4'b0000: if(RxD_bit_inv) state <= 4'b1000;  // start bit found?

4'b1000: if(next_bit) state <= 4'b1001;  // bit 0

4'b1001: if(next_bit) state <= 4'b1010;  // bit 1

4'b1010: if(next_bit) state <= 4'b1011;  // bit 2

4'b1011: if(next_bit) state <= 4'b1100;  // bit 3

4'b1100: if(next_bit) state <= 4'b1101;  // bit 4

4'b1101: if(next_bit) state <= 4'b1110;  // bit 5

4'b1110: if(next_bit) state <= 4'b1111;  // bit 6

4'b1111: if(next_bit) state <= 4'b0001;  // bit 7

4'b0001: if(next_bit) state <= 4'b0000;  // stop bit

default: state <= 4'b0000;

endcase

 

//使用一个移位寄存器来存储接收到的数据

reg [7:0] RxD_data;

always @(posedge clk)

if(Baud8Tick && next_bit && state[3]) RxD_data <= {~RxD_bit_inv, RxD_data[7:1]};

 

reg RxD_data_ready, RxD_data_error;

always @(posedge clk)

begin

RxD_data_ready <= (Baud8Tick && next_bit && state==4'b0001 && ~RxD_bit_inv); 

RxD_data_error <= (Baud8Tick && next_bit && state==4'b0001 &&  RxD_bit_inv);

end

 

reg [4:0] gap_count;

always @(posedge clk)

      if (state!=0) gap_count<=5'h00;

           else if (Baud8Tick & ~gap_count[4]) gap_count <= gap_count + 5'h01;

 

assign RxD_idle = gap_count[4];

 

reg RxD_endofpacket;

 

always @(posedge clk)

        RxD_endofpacket <= Baud8Tick & (gap_count==5'h0F);

 

endmodule

 

测试代码如下：

 

wire RxD_data_ready;

wire [7:0]RxD_data;

wire RxD_endofpacket;

wire RxD_idle;

 

reg [7:0]RxD_data_tmp;

 

//保存接收到的串口数据

always @(posedge clk)

begin

if(RxD_data_ready)

           RxD_data_tmp <= RxD_data;

else

           RxD_data_tmp <= RxD_data_tmp;

end

 

//把串口接收到的数据和LED绑定，通过串口数据控制LED的状态

assign led0 = RxD_data_tmp[0];   // bit0

assign led1 = RxD_data_tmp[1];   //bit1

assign led2 = RxD_data_tmp[2];   //bit2

assign led3 = RxD_data_tmp[3];   //bit3          

 

//例化串口接收模块

async_receiver async_receiver_inst(

                                                                   .clk(clk),

                                                                   .RxD(uart_tx),

                                                                   .RxD_data_ready (RxD_data_ready),

                                                                   .RxD_data (RxD_data),

                                                                   .RxD_endofpacket (RxD_endofpacket),

                                                                   .RxD_idle(RxD_idle));

 

   

测试结果：

有空拍几张效果图上来，哈哈

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