帧结构的串行数据接收器—

帧结构的串行数据接收器——Verilog实现

用Verilog 实现一个帧结构的串行数据接收器；

串行数据输入为：NRZ数据加位时钟（BCL）格式，高位在前
帧结构为：8位构成一个字，64字构成一个帧。每帧的第一个字为同步字。
同步字图案存储在可由CPU读写的同步字寄存器（端口地址00H）中
串行接受器在连续检测到3个同步图案后，开始接受数据，并向CPU中传送数据。串行数据接收器每接收到一个字，先送到数据寄存器中， CPU以I/O读方式，从数据寄存器中读取数据（端口地址为01H）
若数据寄存器已满，再有数据写入时，则覆盖原有的数据。在数据寄存器为空时，CPU从数据寄存器中读到的数据将是同步字寄存器的内容。
在接收数据过程中，若任何一帧的同步字不匹配，则进入到头步状态，停止数据接收。失步后，必须重新同步（连续检测到3个同步图案），然后开始新的数据接收。
寄存器的读写采用和8031类似的控制方式，有关信号包括：双向数据（DATA[7:0]）、I/O地址（ADDR[7:0]）、I/O写(IOW)、和I/O读(IOR),其中IOW和IOR都是低电平有效
设计者可以根据需要增加其它的输入输出信号

设计分析

端口
输入数据和时钟之间的关系
帧结构
8位构成一个字，64字构成一个帧。每帧的第一个字为同步字。
连续检测到三个同步帧，即连续三个同步头和同步图案一样的帧，才开始进行数据接收
详细设计-工作阶段非常明显
- 失步阶段：检测同步头，根据情况确定是否转入同步状态
- 同步阶段：检测同步头，如果匹配则接收数据，仍然处于同步阶段；否则转入失步状态。
- 注意：是失步态下检测的一个同步字时需要每个时钟周期都要进行比较
实现思路：采用状态机进行实现
- 状态转换的控制
  - 计数器：接收位计数–>字，字计数–>数据帧
  - 比较器：接收数据与同步字的比较
两个状态

该状态转换关系从功能需求很容易得出
难点：需要检测三个连续的同步帧才能从失步态到同步态
控制不清晰
四状态划分

实现难点：每个帧持续8*64个时钟周期，其中第8个时钟周期结束需要同步头比较，后面的504个时钟周期接收数据（同步态）或空等（失步态）
8个状态
- 在每个状态，省略了自身状态转移的情况
- 每个R_Headx状态持续八个周期（Read_Head1）除外
- 每个R_Datax状态持续504个周期
- 需要设计一个记8和一个记504的计数器辅助进行控制
代码部分
完整代码

`timescale 1ns / 1psmodule S2P (reset,clk,serial_in,ior,iow,address,data,cnt
);input           reset;input           clk;input           serial_in;input           ior;input           iow;input   [7:0]   address;inout   [7:0]   data;output          cnt;reg     [7:0]   Data;reg             counter8_en,counter504_en,counter8_clr,counter504_clr;reg     [2:0]   counter8;reg     [8:0]   counter504;reg     [7:0]   shifter,data_reg,sync_word;reg     [2:0]   pres_state,next_state;reg             cnt;parameter R_Head1 = 3'b000,R_Data1 = 3'b001,R_Head2 = 3'b010,R_Data2 = 3'b011,R_Head3 = 3'b100,R_Data3 = 3'b101,R_Head = 3'b110,R_Data = 3'b111;   //状态机always @(posedge reset or posedge clk) beginif (reset) pres_state = R_Head1;else pres_state = next_state;endalways @(pres_state,shifter,counter8,counter504) begincase(pres_state)R_Head1: if (shifter == sync_word) next_state = R_Data1;else next_state = R_Head1;R_Data1: if (counter504 == 9'b0) next_state = R_Head2;else next_state = R_Data1;R_Head2: if (counter8 == 3'b0) beginif (shifter == sync_word) next_state = R_Data2;else next_state = R_Head1;end else next_state = R_Head2;R_Data2: if (counter504 == 9'b0) next_state = R_Head3;else next_state = R_Data2;R_Head3: if (counter8 == 3'b0) beginif (shifter == sync_word) next_state = R_Data3;else next_state = R_Head1;end else next_state = R_Head3; R_Data3: if (counter504 == 9'b0) next_state = R_Head;else next_state = R_Data3;R_Head: if (counter8 == 3'b0) beginif (shifter == sync_word) next_state = R_Data;else next_state = R_Head1;end else next_state = R_Head;R_Data: if (counter504 == 9'b0) next_state = R_Head;else  next_state = R_Data;default: next_state = R_Head1;endcaseendalways @(next_state,pres_state) beginif (pres_state == R_Data) cnt = 1'b1;else cnt = 1'b0;end // 移位器和计数器always @(posedge reset or posedge clk) beginif (reset) shifter = 8'b0;else shifter = {serial_in,shifter[7:1]};endalways @(posedge clk  or posedge reset) beginif (reset) counter8 = 3'b111;else beginif (counter8_clr) counter8 = 3'b111;else if (counter8_en)counter8 = counter8 - 1; endendalways @(posedge clk  or posedge reset) beginif (reset) counter504 = 9'b1_1111_0111;else beginif (counter504_clr) counter504= 9'b1_1111_0111;else if (counter504_en)counter504 = counter504 - 1; endend// 计数器计数使能和清零信号生成always @(pres_state) beginif (pres_state == R_Data1 || pres_state == R_Data2 || pres_state == R_Data3 || pres_state == R_Data)counter8_clr = 1'b1;else counter8_clr = 1'b0;endalways @(pres_state) beginif (pres_state == R_Head2 || pres_state == R_Head3 || pres_state == R_Head) counter8_en = 1'b1;else counter8_en = 1'b0;endalways @(pres_state) beginif (pres_state == R_Head1 || pres_state == R_Head2 || pres_state == R_Head3 || pres_state == R_Head) counter504_clr = 1'b1;else counter504_clr = 1'b0;endalways @(pres_state) beginif (pres_state == R_Data1 || pres_state == R_Data2 || pres_state == R_Data3 || pres_state == R_Data) counter504_en = 1'b1;else counter504_en = 1'b0;end//数据寄存器读写和同步字寄存器的写入always @(posedge reset or posedge clk)if (reset) data_reg = 8'b0;else if (counter504_en == 1'b1 && counter504[2:0] == 3'b0) data_reg = shifter;always @(posedge reset or posedge clk) beginif (reset) sync_word = 8'b0000_0001;else if (iow == 1'b0 && address == 8'b0) sync_word = data;endalways @(ior or address or data_reg) if (ior == 1'b0 && address == 8'b1) Data = data_reg;else Data = 8'bz;assign data = Data;endmodule

Testbench

`timescale 1ns / 1ps
module tb_S2P;reg       reset;reg       clk;reg       serial_in;reg       ior;reg       iow;reg [7:0] address;wire[7:0] data;wire       cnt;S2P s2p (.reset(reset),.clk(clk),.serial_in(serial_in),.ior(ior),.iow(iow),.address(address),.data(data),.cnt(cnt));reg [7:0] d;assign data = (ior == 1'b1)?d:8'bz;//assign data = (ior == 1'b0 &&address == 8'b1)?d:8'bz;always begin#10 clk = ~clk; endinteger i;initial beginserial_in = 1'bZ;#10 ; while (1) beginior = 1'b1;#20; serial_in = 1'b0;#20; serial_in = 1'b1;#20; serial_in = 1'b1;#20; serial_in = 1'b1;#20; serial_in = 1'b1;#20; serial_in = 1'b1;#20; serial_in = 1'b1;#20; serial_in = 1'b0;for (i = 1;i <= 63*8;i = i + 1)#20 serial_in = {$random}%2;end  endinitial beginclk = 0;reset = 1'b1;#20#5 reset = 1'b0;endinitial beginior = 1'b1;//address = 8'b0;//s2p.pres_state = 3'b1;iow = 1'b1;address = 8'b0;d = 8'b01111110;#20#5;iow = 1'b0;//address = 8'b0;#10;address = 8'b0000_0001;//ior = 1'b0;#5 iow = 1'b1;endalways @(cnt) beginior = ~cnt;endinitial begin#20#101000;$finish;end
endmodule