在FPGA中使用Verilog实现I2C通信

按照I2C标准的官方时序

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];