1. 串口接收原理
基本原理：通过数据起始位判断要是否要开始接收的数据，通过采样的方式确定每一位数据是0还是1。
如何判断数据起始位到来：通过边沿检测电路检测起始信号的下降沿
如何采样：一位数据采多次，统计得到高电平出现的次数，次数多的就是该位的电平值
2. 自己写的代码（不完善）
设计代码
cpp
module uart_byte_rx(
clk,
rstn,
uart_byte_rx,
blaud_set,
data,
rx_done
);
input clk;
input rstn;
input uart_byte_rx;
input blaud_set;
output reg [7:0] data;
output reg rx_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;
endcase
reg [1:0] test;
reg get_en;
always@(posedge clk or negedge rstn) //边沿检测，使能后续的采样
if(!rstn) begin
data <= 0;
test <= 0;
get_en <= 0;
rx_done <= 0;
end
else begin
test[0] <= uart_byte_rx;
test[1] <= test[0];
if((test[0] ==0 )&&(test[1] == 1))
get_en <= 1;
rx_done <= 0;
end
reg [17:0] div_cnt;
reg [3:0] counter;
reg [3:0] tx_counter;
always@(posedge clk or negedge rstn) //计数时钟，一个计数周期代表一位数据
if(!rstn)
div_cnt <= 0;
else if(get_en)begin
if(div_cnt == 434 - 1)
div_cnt <= 0;
else
div_cnt <= div_cnt + 1'd1;
end
wire bps_clk;
assign bps_clk = (div_cnt == 1);
always@(posedge clk or negedge rstn) //数据段，包含起始位和终止位，共十段
if(!rstn)
tx_counter <= 0;
else if(get_en)begin
if(tx_counter == 11)
tx_counter <= 0;
else if(div_cnt == 1)
tx_counter <= tx_counter + 1'd1;
end
always@(posedge clk or negedge rstn) //数据采样，每段数据采样8次。
if(!rstn)
counter <= 0;
else if(div_cnt == 3)
counter <= 0;
else if((div_cnt == 1*433/8 - 10)||
(div_cnt == 2*433/8 - 10)||
(div_cnt == 3*433/8 - 10)||
(div_cnt == 4*433/8 - 10)||
(div_cnt == 5*433/8 - 10)||
(div_cnt == 6*433/8 - 10)||
(div_cnt == 7*433/8 - 10)||
(div_cnt == 8*433/8 - 10))
counter <= counter + uart_byte_rx;
always@(posedge clk or negedge rstn) //
if(!rstn)
counter <= 0;
else if(div_cnt == 2)
case(tx_counter)
2:if(counter > 4 )data[0] <= 1; else if(counter <4) data[0] <= 0;
3:if(counter > 4 )data[1] <= 1; else if(counter <4) data[1] <= 0;
4:if(counter > 4 )data[2] <= 1; else if(counter <4) data[2] <= 0;
5:if(counter > 4 )data[3] <= 1; else if(counter <4) data[3] <= 0;
6:if(counter > 4 )data[4] <= 1; else if(counter <4) data[4] <= 0;
7:if(counter > 4 )data[5] <= 1; else if(counter <4) data[5] <= 0;
8:if(counter > 4 )data[6] <= 1; else if(counter <4) data[6] <= 0;
9:if(counter > 4 )data[7] <= 1; else if(counter <4) data[7] <= 0;
11:begin rx_done <= 1; get_en <= 0; div_cnt <= 0; end
default: begin rx_done <= 0; data <= data; end
endcase
endmodule仿真波形
3. 看完视频后写的代码（完善）
设计代码
3.1 需学习的点：
1.将div_cnt划分为最小时间段
2.某些判断信号直接用assign利用，而不需要利用寄存器
3.仿真代码中task的使用
cpp
module uart_byte_rx1(
clk,
rstn,
blaud_set,
uart_rx,
data,
rx_done
);
input clk;
input rstn;
input [2:0]blaud_set;
input uart_rx;
output reg [7:0] data;
output rx_done;
reg [8:0] bps_dr;
always@(*)
case(blaud_set)
0:bps_dr = 1000000000/9600/16/20;
1:bps_dr = 1000000000/19200/16/20;
2:bps_dr = 1000000000/38400/16/20;
3:bps_dr = 1000000000/57600/16/20;
4:bps_dr = 1000000000/115200/16/20;
default : bps_dr = 1000000000/9600/16/20;
endcase
//边沿信号检测
reg [1:0] uart_rx_r; //用两位寄存器分别存储两个时间沿的uart_rx信号
always@(posedge clk) begin
uart_rx_r[0] <= uart_rx;
uart_rx_r[1] <= uart_rx_r[0];
end
//将两位寄存器的值直接通过导线输出进行判断（不需要再使用寄存器）
wire nedge_uart_rx; //掌握一下这个方法，之前一直使用的是寄存器
//法一：
//assign nedge_uart_rx = ((uart_rx_r[0] == 0)&&(uart_rx_r == 1));
//法二：
assign nedge_uart_rx = (uart_rx_r == 2'b10);
reg rx_en;
always@(posedge clk or negedge rstn)
if(!rstn)
rx_en <= 0;
else if(nedge_uart_rx)
rx_en <= 1;
else if(rx_done)
rx_en <= 0;
//周期计数器
reg [8:0] div_cnt;
always@(posedge clk or negedge rstn)
if(!rstn)
div_cnt <= 0;
else if(rx_en) begin
if(div_cnt == bps_dr - 1)
div_cnt <= 0;
else
div_cnt <= div_cnt + 1'd1;
end
else
div_cnt <= 0;
wire [3:0]bps_clk_16x; //（一定要记得加位宽）采样信号，这种写法很灵活
assign bps_clk_16x = bps_dr/2; //采样每一段的中点值，同时也可以用它来计数。
//发送一字节的数据有需要十个数据位，每位数据有16个小段供采样,共160
reg [7:0]bps_cnt;
always@(posedge clk or negedge rstn)
if(!rstn)
bps_cnt <= 0;
else if(rx_en) begin
if(bps_cnt == 159)
bps_cnt <= 0;
else if(div_cnt ==bps_clk_16x)
bps_cnt <= bps_cnt + 1'd1;
end
else
bps_cnt <= 0;
reg[2:0] r_data[7:0];//二维数据，代表八个r_data，每个r_data有3位寄存器存储数值。
reg[2:0] sta_data;
reg[2:0] sto_data;
always@(posedge clk or negedge rstn)
if(!rstn)begin
sta_data <= 0;
sto_data <= 0;
r_data[0] <= 0; //语法规定，二维数组赋值要分开赋值
r_data[1] <= 0;
r_data[2] <= 0;
r_data[3] <= 0;
r_data[4] <= 0;
r_data[5] <= 0;
r_data[6] <= 0;
r_data[7] <= 0;
end
else if(div_cnt == bps_clk_16x - 1)
case(bps_cnt) //下面合在一起的写法是允许的
0:begin
r_data[0] <= 0;
r_data[1] <= 0;
r_data[2] <= 0;
r_data[3] <= 0;
r_data[4] <= 0;
r_data[5] <= 0;
r_data[6] <= 0;
r_data[7] <= 0;
end
5,6,7,8,9,10,11: sta_data <= sta_data + uart_rx;
21,22,23,24,25,26,27: r_data[0] <= r_data[0] + uart_rx;
37,38,39,40,41,42,43: r_data[1] <= r_data[1] + uart_rx;
53,54,55,56,57,58,59: r_data[2] <= r_data[2] + uart_rx;
69,70,71,72,73,74,75: r_data[3] <= r_data[3] + uart_rx;
85,86,87,88,89,90,91: r_data[4] <= r_data[4] + uart_rx;
101,102,103,104,105,106,107: r_data[5] <= r_data[5] + uart_rx;
117,118,119,120,121,122,123: r_data[6] <= r_data[6] + uart_rx;
133,134,135,136,137,138,139: r_data[7] <= r_data[7] + uart_rx;
149,150,151,152,153,154,155: sto_data <= sto_data + uart_rx;
default:;
endcase
reg rx_done;
always@(posedge clk or negedge rstn)
if(!rstn)
rx_done <= 0;
else if(bps_cnt == 159) begin
rx_done <= 1;
end
else
rx_done <= 0;
//数据接收完成后赋值给data输出
always@(posedge clk or negedge rstn)
if(!rstn)
data <= 0;
else if(rx_done)begin
data[0] <= (r_data[0] >= 4 ) ? 1 : 0; //可换种写法，写法如下
data[1] <= (r_data[1] >= 4 ) ? 1 : 0;
data[2] <= (r_data[2] >= 4 ) ? 1 : 0;
data[3] <= (r_data[3] >= 4 ) ? 1 : 0;
data[4] <= (r_data[4] >= 4 ) ? 1 : 0;
data[5] <= (r_data[5] >= 4 ) ? 1 : 0;
data[6] <= (r_data[6] >= 4 ) ? 1 : 0;
data[7] <= (r_data[7] >= 4 ) ? 1 : 0;
end
// data[1] <= r_data[1][2]
// 0:3'd000
// 1:3'd001
// 2:3'd010
// 4:3'd100
// 5:3'd101
// 6:3'd110
// 7:3'd111 利用第3位的区别给data赋值
endmodule仿真代码
cpp
`timescale 1ns/1ns
module uart_byte_rx1_tb();
reg clk;
reg rstn;
reg uart_rx;
wire [2:0]blaud_set;
wire [7:0]data;
wire rx_done;
uart_byte_rx1 uart_byte_rx_inst1(
.clk(clk),
.rstn(rstn),
.blaud_set(blaud_set),
.uart_rx(uart_rx),
.data(data),
.rx_done(rx_done)
);
assign blaud_set = 3'd4;
initial clk = 1;
always #10 clk = ~clk;
initial begin
rstn = 0;
uart_rx = 1;
#201;
rstn = 1;
#200;
uart_tx_byte(8'h5a);
@(posedge rx_done)
#5000;
uart_tx_byte(8'ha5);
@(posedge rx_done)
#5000;
uart_tx_byte(8'h86);
@(posedge rx_done)
#5000;
$stop;
end
task uart_tx_byte;
input [7:0] tx_data;
begin
uart_rx = 1;
#20;
uart_rx = 0;
#8680;
uart_rx = tx_data[0];
#8680;
uart_rx = tx_data[1];
#8680;
uart_rx = tx_data[2];
#8680;
uart_rx = tx_data[3];
#8680;
uart_rx = tx_data[4];
#8680;
uart_rx = tx_data[5];
#8680;
uart_rx = tx_data[6];
#8680;
uart_rx = tx_data[7];
end
endtask
endmodule仿真波形
