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        通用异步收发传输器（ Universal Asynchronous Receiver/Transmitter， UART）是一种异步收发传输器，其在数据发送时将并行数据转换成串行数据来传输， 在数据接收时将接收到的串行数据转换成并行数据， 可以实现全双工传输和接收。它包括了 RS232、 RS449、 RS423、RS422 和 RS485 等接口标准规范和总线标准规范。 换句话说， UART 是异步串行通信的总称。而 RS232、 RS449、 RS423、 RS422 和 RS485 等，是对应各种异步串行通信口的接口标准和总线标准，它们规定了通信口的电气特性、传输速率、连接特性和接口的机械特性等内容。

1. 09AB 基于FPGA的串口（UART）发送实验

1. 串口通信模块设计的目的是用来发送数据的，因此需要有一个数据输入端口。
2. 串口通信，支持不同的波特率，所以需要有一个波特率设置端口。
3. 串口通信的本质就是将8位的并行数据，在不同的时刻传输并行数据的不同位，通过一根信号线将八位并行数据全部传出。
4. 串口通信以1位的低电平标志串行传输的开始，待8位数据传输完成之后，再以1位的高电平标志传输的结束。
5. 控制信号，控制并转串模块什么时候开始工作，什么时候一个数据发送完成？所以需要一个发送开始信号，以及一个发送完成信号

设计代码

1. bps_cnt在空闲状态下保持为0，而bps_cnt为0会使得uart_tx为0，为了解决该问题，我们避开空闲状态下的bps_cnt=0，使bps_cnt从1开始判定。
2. 但是这又会导致bps_cnt从0到1存在空闲，发送起始位时会延后一段数据位，于是我们将基础计数时间改为1时counter1开始加一。
3. 为了出现bps_clk脉冲信号，当(div_cnt == (bps_dr - 1)成立时会输出1，我们利用该特性作为我们的脉冲信号。
4. 我们要输入八位数据以及起始位和终止位共十位数据，为了保证十位数据完整输出，我们需要设置到第十一位停止，发送tx_done信号。
5. 输入信号不能是reg类型，否则综合设计代码时报错：Non-net port key_in cannot be of mode input，写代码时遇到的问题。

module uart_byte_tx(clk,rstn,blaud_set,data,send_en,uart_tx,tx_done
);input clk;input rstn;input [2:0]blaud_set;input [7:0]data;input send_en;output reg uart_tx;output tx_done;//Blaud_set = 0时，波特率 = 9600；//Blaud_set = 1时，波特率 = 19200；//Blaud_set = 2时，波特率 = 38400；//Blaud_set = 3时，波特率 = 57600；//Blaud_set = 4时，波特率 = 115200；reg[17:0] bps_dr;always@(*)case(blaud_set)0: bps_dr = 1000000000/9600/20;1: bps_dr = 1000000000/19200/20;2: bps_dr = 1000000000/38400/20;3: bps_dr = 1000000000/57600/20;4: bps_dr = 1000000000/115200/20;endcasewire bps_clk;assign bps_clk = (div_cnt == (bps_dr - 1)); //3.为了出现bps_clk脉冲信号reg[17:0] div_cnt;always@(posedge clk or negedge rstn)if(!rstn)div_cnt <= 0;else if(send_en)beginif(bps_clk)div_cnt <= 0;elsediv_cnt <= div_cnt + 1'd1;endelsediv_cnt <= 0;    reg[3:0] bps_cnt;    always@(posedge clk or negedge rstn)if(!rstn)bps_cnt <= 0;else if(send_en)beginif(bps_cnt == 11)bps_cnt <= 0;else if(div_cnt == 1) //注意2bps_cnt <= bps_cnt + 4'd1;endelsebps_cnt <= 0;reg tx_done;always@(posedge clk or negedge rstn)if(!rstn)uart_tx <= 1'd1;else case(bps_cnt)1: begin uart_tx <= 1'd0; tx_done <= 0; end //注意12: uart_tx <= data[0];3: uart_tx <= data[1];4: uart_tx <= data[2];5: uart_tx <= data[3];6: uart_tx <= data[4];7: uart_tx <= data[5];8: uart_tx <= data[6];9: uart_tx <= data[7];10: uart_tx <= 1'd1;11: begin uart_tx <= 1'd1; tx_done <= 1; end //注意4default: uart_tx <= 1'd1;endcaseendmodule

仿真代码：

`timescale 1ns/1nsmodule uart_byte_tx_tb();reg clk;reg rstn;reg [2:0] blaud_set;reg [7:0] data;reg send_en;wire uart_tx;wire tx_done;    uart_byte_tx uart_byte_tx_inst(.clk(clk),.rstn(rstn),.blaud_set(blaud_set),.data(data),.send_en(send_en),.uart_tx(uart_tx),.tx_done(tx_done));initial clk = 1;always #10 clk = ~clk;initial beginrstn = 0;data = 0;send_en = 0;blaud_set = 4;#201;rstn = 1;#100data = 8'h57;send_en = 1;#20;@(posedge tx_done);send_en = 0;#20000;data = 8'h75;send_en = 1;#20;@(posedge tx_done);#20000;send_en = 0;$stop;endendmodule

仿真波形

2. 10 串口发送应用之发送数据

使用上一节课设计的串口发送模块，设计一个数据发送器，每10ms以115200的波特率发送一个数据，每次发送的数据比前一个数据大一（计数器）。

在实际应用的时候，我们不能通过counter去控制data，只能通过控制信号去控制。要求就是通过tx_done和send_en这两个控制信号，控制我要发送的数据内容。

思路：通过顶层模块调用uart_byte_tx发送模块来发送数据，将顶层模块命名为uart_tx_test。

 设计代码（第一版，不完善）

2.1 直接使用上一节的uart_byte_tx模块：

module uart_tx_test(clk,rstn,uart_tx
);input clk;input rstn;output uart_tx;reg [7:0] data;reg send_en;uart_byte_tx uart_byte_tx_inst(.clk(clk),.rstn(rstn),.blaud_set(3'd4),.data(data),.send_en(send_en),.uart_tx(uart_tx),.tx_done(tx_done));//10ms周期计数器reg [18:0] counter;always@(posedge clk or negedge rstn)if(!rstn)counter <= 0;else if(counter == 499999)counter <= 0;elsecounter <= counter + 1'd1;always@(posedge clk or negedge rstn)if(!rstn)send_en <= 0;else if(counter == 0)send_en <= 1;else if(tx_done)send_en <= 0;always@(posedge clk or negedge rstn)if(!rstn)data <= 8'b0000_0000;else if(tx_done)data <= data + 1'd1;endmodule

module uart_byte_tx(clk,rstn,blaud_set,data,send_en,uart_tx,tx_done
);input clk;input rstn;input [2:0]blaud_set;input [7:0]data;input send_en;output reg uart_tx;output tx_done;//Blaud_set = 0时，波特率 = 9600；//Blaud_set = 1时，波特率 = 19200；//Blaud_set = 2时，波特率 = 38400；//Blaud_set = 3时，波特率 = 57600；//Blaud_set = 4时，波特率 = 115200；reg[17:0] bps_dr;always@(*)case(blaud_set)0: bps_dr = 1000000000/9600/20;1: bps_dr = 1000000000/19200/20;2: bps_dr = 1000000000/38400/20;3: bps_dr = 1000000000/57600/20;4: bps_dr = 1000000000/115200/20;endcasewire bps_clk;assign bps_clk = (div_cnt == (bps_dr - 1)); reg[17:0] div_cnt;always@(posedge clk or negedge rstn)if(!rstn)div_cnt <= 0;else if(send_en)beginif(bps_clk)div_cnt <= 0;elsediv_cnt <= div_cnt + 1'd1;endelsediv_cnt <= 0;    reg[3:0] bps_cnt;    always@(posedge clk or negedge rstn)if(!rstn)bps_cnt <= 0;else if(send_en)beginif(bps_cnt == 11)bps_cnt <= 0;else if(div_cnt == 1) bps_cnt <= bps_cnt + 4'd1;endelsebps_cnt <= 0;reg tx_done;always@(posedge clk or negedge rstn)if(!rstn)uart_tx <= 1'd1;else case(bps_cnt) //不完善1: begin uart_tx <= 1'd0; tx_done <= 0; end 2: uart_tx <= data[0];3: uart_tx <= data[1];4: uart_tx <= data[2];5: uart_tx <= data[3];6: uart_tx <= data[4];7: uart_tx <= data[5];8: uart_tx <= data[6];9: uart_tx <= data[7];10: uart_tx <= 1'd1;11: begin uart_tx <= 1'd1; tx_done <= 1; enddefault: uart_tx <= 1'd1;endcaseendmodule

仿真代码

`timescale 1ns / 1psmodule uart_tx_test_tb();reg clk;reg rstn;wire uart_tx;uart_tx_test uart_tx_test_inst(.clk(clk),.rstn(rstn),.uart_tx(uart_tx));initial clk = 1;always #10 clk = ~clk;initial beginrstn = 0;#201;rstn = 1;#200000000$stop;endendmodule

仿真波形

data确实在一直加一，但是data并未发出（uart_tx一直保持为1）

2.2 修改tx_done逻辑后（能运行）

设计代码

module uart_tx_test(clk,rstn,uart_tx
);input clk;input rstn;output uart_tx;reg [7:0] data;reg send_en;uart_byte_tx uart_byte_tx_inst(.clk(clk),.rstn(rstn),.blaud_set(3'd4),.data(data),.send_en(send_en),.uart_tx(uart_tx),.tx_done(tx_done));//10ms周期计数器reg [18:0] counter;always@(posedge clk or negedge rstn)if(!rstn)counter <= 0;else if(counter == 499999)counter <= 0;elsecounter <= counter + 1'd1;always@(posedge clk or negedge rstn)if(!rstn)send_en <= 0;else if(counter == 0)send_en <= 1;else if(tx_done)send_en <= 0;always@(posedge clk or negedge rstn)if(!rstn)data <= 8'b0000_0000;else if(tx_done)data <= data + 1'd1;endmodule

module uart_byte_tx(clk,rstn,blaud_set,data,send_en,uart_tx,tx_done
);input clk;input rstn;input [2:0]blaud_set;input [7:0]data;input send_en;output reg uart_tx;output tx_done;//Blaud_set = 0时，波特率 = 9600；//Blaud_set = 1时，波特率 = 19200；//Blaud_set = 2时，波特率 = 38400；//Blaud_set = 3时，波特率 = 57600；//Blaud_set = 4时，波特率 = 115200；reg[17:0] bps_dr;always@(*)case(blaud_set)0: bps_dr = 1000000000/9600/20;1: bps_dr = 1000000000/19200/20;2: bps_dr = 1000000000/38400/20;3: bps_dr = 1000000000/57600/20;4: bps_dr = 1000000000/115200/20;endcasewire bps_clk;assign bps_clk = (div_cnt == 1);reg[17:0] div_cnt;always@(posedge clk or negedge rstn)if(!rstn)div_cnt <= 0;else if(send_en)beginif(div_cnt == (bps_dr - 1))div_cnt <= 0;elsediv_cnt <= div_cnt + 1'd1;endelsediv_cnt <= 0;    reg[3:0] bps_cnt;    always@(posedge clk or negedge rstn)if(!rstn)bps_cnt <= 0;else if(send_en)beginif(bps_cnt == 11)bps_cnt <= 0;else if(div_cnt == 1)bps_cnt <= bps_cnt + 4'd1;endelsebps_cnt <= 0;reg tx_done;always@(posedge clk or negedge rstn)if(!rstn)uart_tx <= 1'd1;else case(bps_cnt)0: tx_done <= 0;1: uart_tx <= 1'd0;2: uart_tx <= data[0];3: uart_tx <= data[1];4: uart_tx <= data[2];5: uart_tx <= data[3];6: uart_tx <= data[4];7: uart_tx <= data[5];8: uart_tx <= data[6];9: uart_tx <= data[7];10: uart_tx <= 1'd1;11: begin uart_tx <= 1'd1; tx_done <= 1; enddefault: uart_tx <= 1'd1;endcaseendmodule

仿真波形

 

2.3 完善串口模块，使其能接入数据采集模块

• 数据采集模块data_gen，每采集到一个数据data result[7:0]，会产生一个data_done的脉冲信号，uart串口在就接收到data_done的脉冲信号后会将data result[7:0]发送出去。
• 思路：我们可以利用脉冲信号data_done来使能我们的send_en信号，然后将接收到的data result[7:0]通过串口发送
• 为了模拟这个过程，我们让顶层uart_tx_test每隔10ms产生一个data[7:0]和一个send_go的单脉冲信号发送给uart_byte_tx模块。让uart_byte_tx模块根据send_go脉冲信号去发数据即可。
• 为了防止数据发送途中data发生变化，我们在接收到send_go信号后，先将data存储起来，即声明一个r_data[7:0]，使将data[7:0]的值赋值给r_data[7:0]。

 

 设计代码

module uart_tx_test1(clk,rstn,uart_tx
);input clk;input rstn;output uart_tx;reg [7:0] data;reg send_go;uart_byte_tx uart_byte_tx_inst(.clk(clk),.rstn(rstn),.blaud_set(3'd4),.data(data),.send_go(send_go),.uart_tx(uart_tx),.tx_done(tx_done));//10ms周期计数器reg [18:0] counter;always@(posedge clk or negedge rstn)if(!rstn)counter <= 0;else if(counter == 499999)counter <= 0;elsecounter <= counter + 1'd1;always@(posedge clk or negedge rstn)if(!rstn)send_go <= 0;else if(counter == 0)send_go <= 1;elsesend_go <= 0;always@(posedge clk or negedge rstn)if(!rstn)data <= 8'b0000_0000;else if(tx_done)data <= data + 1'd1;endmodule

module uart_byte_tx(clk,rstn,blaud_set,data,send_go,uart_tx,tx_done
);input clk;input rstn;input [2:0]blaud_set;input [7:0]data;input send_go;output reg uart_tx;output tx_done;//Blaud_set = 0时，波特率 = 9600；//Blaud_set = 1时，波特率 = 19200；//Blaud_set = 2时，波特率 = 38400；//Blaud_set = 3时，波特率 = 57600；//Blaud_set = 4时，波特率 = 115200；reg[17:0] bps_dr;always@(*)case(blaud_set)0: bps_dr = 1000000000/9600/20;1: bps_dr = 1000000000/19200/20;2: bps_dr = 1000000000/38400/20;3: bps_dr = 1000000000/57600/20;4: bps_dr = 1000000000/115200/20;endcasereg [7:0] r_data;always@(posedge clk)if(send_go)r_data <= data;elser_data <= r_data;reg send_en;  always@(posedge clk or negedge rstn)if(!rstn)send_en <= 0;else if(send_go)send_en <= 1;else if(tx_done)send_en <= 0;wire bps_clk;assign bps_clk = (div_cnt == 1);reg[17:0] div_cnt;always@(posedge clk or negedge rstn)if(!rstn)div_cnt <= 0;else if(send_en)beginif(div_cnt == (bps_dr - 1))div_cnt <= 0;elsediv_cnt <= div_cnt + 1'd1;endelsediv_cnt <= 0;    reg[3:0] bps_cnt;    always@(posedge clk or negedge rstn)if(!rstn)bps_cnt <= 0;else if(send_en)beginif(bps_cnt == 11)bps_cnt <= 0;else if(div_cnt == 1)bps_cnt <= bps_cnt + 4'd1;endelsebps_cnt <= 0;reg tx_done;always@(posedge clk or negedge rstn)if(!rstn)uart_tx <= 1'd1;else case(bps_cnt)0: tx_done <= 0;1: uart_tx <= 1'd0;2: uart_tx <= r_data[0];3: uart_tx <= r_data[1];4: uart_tx <= r_data[2];5: uart_tx <= r_data[3];6: uart_tx <= r_data[4];7: uart_tx <= r_data[5];8: uart_tx <= r_data[6];9: uart_tx <= r_data[7];10: uart_tx <= 1'd1;11: begin uart_tx <= 1'd1; tx_done <= 1; enddefault: uart_tx <= 1'd1;endcaseendmodule

仿真代码

`timescale 1ns / 1psmodule uart_tx_test_tb();reg clk;reg rstn;wire uart_tx;uart_tx_test1 uart_tx_test_inst(.clk(clk),.rstn(rstn),.uart_tx(uart_tx));initial clk = 1;always #10 clk = ~clk;initial beginrstn = 0;#201;rstn = 1;#200000000$stop;endendmodule

仿真波形

 在开发板上跑程序

调试结果：确实按照每100ms法发一个数据