在FPGA中使用Verilog实现I2C通信

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按照I2C标准的官方时序

FPGA之I2C的实现
可以看出时序看起来很简单，不过它严格的按照时序要求来传送数据，马虎不得的，特别是起始和停止的条件，起始必须要时钟线SCL为高电平时数据线SDA拉低；而停止时必须要时钟线SCL为高电平时数据线SDA拉高；中间的数据的每一位传送都是必须要求在时钟线SCL为高定平时完成；

Verilog HDL程序采用基于状态机的时序设计实现，I2C速度为100KHz，本人开发板的晶振20Mhz。代码有点长，就截取状态机部分好了

`define DEVICE_WRITE 8'b1010_1010 //the data;
reg[7:0] db_r;

parameter IDLE = 4'd0;
parameter START1 = 4'd1;
parameter DATA = 4'd2;
parameter ACK1 = 4'd3;
parameter STOP1 = 4'd11;
parameter STOP2 = 4'd12;

reg[3:0] cstate;
reg sda_r;
reg sda_link;
reg[3:0] num;

always @ (posedge clk or negedge rst_n) begin
if(!rst_n) begin
   cstate <= IDLE;
   sda_r <= 1'b1;
   sda_link <= 1'b0;  //input
   num <= 4'd0;
  end
else
  case (cstate)
   IDLE: begin
      sda_link <= 1'b1;   //output
      sda_r <= 1'b1;
      db_r <= `DEVICE_WRITE;
      cstate <= START1;
     end
   START1: begin
     if(`SCL_HIG) begin
      sda_r <= 1'b0;
      cstate <= DATA;
      num <= 4'd0;
      end
     else cstate <= START1;
    end
   DATA: begin
     if(`SCL_LOW) begin
       if(num == 4'd8) begin
         num <= 4'd0;
         sda_r <= 1'b1;
         sda_link <= 1'b0;  //(input)
         cstate <= ACK1;
        end
       else begin
         cstate <= DATA;
         num <= num+1'b1;
         case (num)
          4'd0: sda_r <= db_r[7];
          4'd1: sda_r <= db_r[6];
          4'd2: sda_r <= db_r[5];
          4'd3: sda_r <= db_r[4];
          4'd4: sda_r <= db_r[3];
          4'd5: sda_r <= db_r[2];
          4'd6: sda_r <= db_r[1];
          4'd7: sda_r <= db_r[0];
          default: ;
         endcase
        end
      end
     else cstate <= DATA;
    end
   ACK1: begin
     if(`SCL_NEG) begin
       cstate <= STOP1;
      end
     else cstate <= ACK1;
    end
   STOP1: begin
     if(`SCL_LOW) begin
       sda_link <= 1'b1;
       sda_r <= 1'b0;
       cstate <= STOP1;
      end
     else if(`SCL_HIG) begin
       sda_r <= 1'b1;
       cstate <= STOP2;
      end
     else cstate <= STOP1;
    end
   STOP2: begin
     if(`SCL_LOW) sda_r <= 1'b1;
     else if(cnt_20ms==20'hffff0) cstate <= IDLE;
     else cstate <= STOP2;
    end
   default: cstate <= IDLE;
   endcase
end

assign sda = sda_link ? sda_r:1'bz;

经过综合，给激励源并仿真后截图

FPGA之I2C的实现

可以看出，时序完全正确，还要注意的就是传完8位数据之后读取的响应位ACK；

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