1. 處理器與外部設(shè)備通信的兩種方式：
并行通信和串行通信
并行通信是指數(shù)據(jù)的各個(gè)位用多條數(shù)據(jù)線同時(shí)進(jìn)行傳輸

優(yōu)點(diǎn)：傳輸速度快
缺點(diǎn)：占用引腳資源多
串行通信是將數(shù)據(jù)分成一位一位的形式在一條傳輸線上逐個(gè)傳輸

優(yōu)點(diǎn)：通信線路簡(jiǎn)單，占用引腳資源少
缺點(diǎn)：傳輸速度慢
2. 串行通信的通信方式：
同步通信和異步通信
同步通信：帶有時(shí)鐘同步信號(hào)的數(shù)據(jù)傳輸；發(fā)送方和接收方在同一時(shí)鐘的控制下，同步傳輸數(shù)據(jù)。

異步通信：不同時(shí)鐘同步信號(hào)的數(shù)據(jù)傳輸。發(fā)送方和接收方使用各自的時(shí)鐘控制數(shù)據(jù)的發(fā)送和接收過(guò)程。

3. 串行通信的傳輸方向
單工：數(shù)據(jù)只能沿一個(gè)方向傳輸
半雙工：數(shù)據(jù)傳輸可以沿兩個(gè)方向，但需要分時(shí)進(jìn)行
全雙工：數(shù)據(jù)可以同時(shí)進(jìn)行雙向傳輸

4. 常見的串行通信接口

5. UART
是一種采用異步串行通信方式的通用異步收發(fā)傳輸器
功能：
它在發(fā)送數(shù)據(jù)時(shí)將并行數(shù)據(jù)轉(zhuǎn)換成串行數(shù)據(jù)來(lái)輸出，在接收數(shù)據(jù)時(shí)將接收到的串行數(shù)據(jù)轉(zhuǎn)換成并行數(shù)據(jù)
a. 協(xié)議層：通信協(xié)議（包括數(shù)據(jù)格式、數(shù)據(jù)速率等）
UART串口通信需要兩根信號(hào)線來(lái)實(shí)現(xiàn)，一根用于串口發(fā)送，另外一根負(fù)責(zé)串口接收

串口通信常用的波特率有9600/19200/38400/115200等
b. 物理層：接口類型，電平標(biāo)準(zhǔn)等
針對(duì)異步串行通信的接口標(biāo)準(zhǔn)有RS232、RS422、RS485

接口定義：


6. 串口通信實(shí)驗(yàn)

module uart_top(input sys_clk,input sys_rst_n,input uart_rxd,output uart_txd );parameter CLK_FREQ = 50000000;parameter UART_BPS = 115200;wire uart_en_w;wire [7:0] uart_data_w;uart_recv #(.CLK_FREQ (CLK_FREQ),.UART_BPS (UART_BPS))u_uart_recv(.sys_clk (sys_clk),.sys_rst_n (sys_rst_n),.uart_rxd (uart_rxd),.uart_done (uart_en_w),.uart_data (uart_data_w));uart_send #(.CLK_FREQ (CLK_FREQ),.UART_BPS (UART_BPS))u_uart_send(.sys_clk (sys_clk),.sys_rst_n (sys_rst_n),.uart_en (uart_en_w),.uart_din (uart_data_w),.uart_data (uart_txd)); endmodulemodule uart_recv(input sys_clk,input sys_rst_n,input uart_rxd,output reg uart_done,output reg [7:0] uart_data );parameter CLK_FREQ = 50000000;parameter UART_BPS = 9600;localparam BPS_CNT = CLK_FREQ/UART_BPS;reg uart_rxd_d0;reg uart_rxd_d1;reg [15:0] clk_cnt;reg [3:0] rx_cnt;reg [7:0] rxdata;reg rx_flag;wire start_flag;//捕獲接收端口下降沿（起始位），得到一個(gè)時(shí)鐘周期的脈沖信號(hào)assign start_flag = uart_rxd_d1 & (~uart_rxd_d0);always @(posedge sys_clk or negedge sys_rst_n) beginif(!sys_rst_n) beginuart_rxd_d0 <= 1'b0;uart_rxd_d1 <= 1'b0;endelse beginuart_rxd_d0 <= uart_rxd;uart_rxd_d1 <= uart_rxd_d0; endendalways @(posedge sys_clk or negedge sys_rst_n) beginif(!sys_rst_n)rx_flag <= 1'b0;else beginif(start_flag)rx_flag <= 1'b1;else if((rx_cnt == 4'd9) && (clk_cnt == BPS_CNT/2))//計(jì)數(shù)到停止位中間時(shí)，停止計(jì)數(shù),因?yàn)檫B續(xù)發(fā)送數(shù)據(jù)的時(shí)候，停止位一個(gè)周期后就是下降沿，又要進(jìn)行下一次數(shù)據(jù)的接收rx_flag <= 1'b0;elserx_flag <= rx_flag;endendalways @(posedge sys_clk or negedge sys_rst_n) beginif(!sys_rst_n) beginclk_cnt <= 16'd0;rx_cnt <= 4'd0;end else if(rx_flag) beginif(clk_cnt < BPS_CNT -1) beginclk_cnt <= clk_cnt + 1'b1;rx_cnt <= rx_cnt;endelse beginclk_cnt <= 16'd0;rx_cnt <= rx_cnt + 1'b1; endendelse beginclk_cnt <= 16'd0;rx_cnt <= 4'd0; endend//根據(jù)接收數(shù)據(jù)技術(shù)來(lái)寄存uart接收端口數(shù)據(jù)always @(posedge sys_clk or negedge sys_rst_n) beginif(!sys_rst_n)rxdata <= 8'd0;else if(rx_flag) beginif(clk_cnt == BPS_CNT/2) begin //計(jì)數(shù)到中間時(shí)數(shù)據(jù)更加穩(wěn)定case(rx_cnt)4'd1:rxdata[0] <= uart_rxd_d1;4'd2:rxdata[1] <= uart_rxd_d1;4'd3:rxdata[2] <= uart_rxd_d1;4'd4:rxdata[3] <= uart_rxd_d1;4'd5:rxdata[4] <= uart_rxd_d1;4'd6:rxdata[5] <= uart_rxd_d1;4'd7:rxdata[6] <= uart_rxd_d1;4'd8:rxdata[7] <= uart_rxd_d1;default:;endcaseendelse rxdata <= rxdata;endelserxdata <= 8'd0;always @(posedge sys_clk or negedge sys_rst_n) beginif(!sys_rst_n) beginuart_data <= 8'd0;uart_done <= 1'b0;endelse if(rx_cnt == 4'd9) beginuart_data <= rxdata;uart_done <= 1'b1; endelse beginuart_data <= 8'd0;uart_done <= 1'b0;endend endmodulemodule uart_send(input sys_clk,input sys_rst_n,input uart_en,output reg uart_txd,output reg [7:0] uart_din );parameter CLK_FREQ = 50000000;parameter UART_BPS = 9600;localparam BPS_CNT = CLK_FREQ/UART_BPS;reg uart_en_d0;reg uart_en_d1;reg [15:0] clk_cnt;reg [3:0] tx_cnt;reg [7:0] tx_data;reg tx_flag;wire en_flag;assign en_flag = ~uart_en_d1 & uart_en_d0;always @(posedge sys_clk or negedge sys_rst_n) beginif(!sys_rst_n) beginuart_en_d0 <= 1'b0;uart_en_d1 <= 1'b0;endelse beginuart_en_d0 <= uart_en;uart_en_d1 <= uart_en_d0; endendalways @(posedge sys_clk or negedge sys_rst_n) beginif(!sys_rst_n) begintx_flag <= 1'b0;tx_data <= 8'd0;endelse if(en_flag) begintx_flag <= 1'b1;tx_data <= uart_din;endelse if((tx_cnt == 4'd9) && (clk_cnt == BPS_CNT/2)) begintx_flag <= 1'b0;tx_data <= 8'd0;endelse begintx_flag <= tx_flag;tx_data <= tx_data;endendalways @(posedge sys_clk or negedge sys_rst_n) beginif(!sys_rst_n) beginclk_cnt <= 16'd0;tx_cnt <= 4'd0;end else if(tx_flag) beginif(clk_cnt < BPS_CNT -1) beginclk_cnt <= clk_cnt + 1'b1;tx_cnt <= tx_cnt;endelse beginclk_cnt <= 16'd0;tx_cnt <= tx_cnt + 1'b1; endendelse beginclk_cnt <= 16'd0;tx_cnt <= 4'd0; endendalways @(posedge sys_clk or negedge sys_rst_n) beginif(!sys_rst_n)uart_txd <= 1'b1;else if(tx_flag) begincase(tx_cnt)4'd0:uart_txd <= 1'b0;4'd1:uart_txd <= tx_data[0];4'd2:uart_txd <= tx_data[1];4'd3:uart_txd <= tx_data[2];4'd4:uart_txd <= tx_data[3];4'd5:uart_txd <= tx_data[4];4'd6:uart_txd <= tx_data[5];4'd7:uart_txd <= tx_data[6];4'd8:uart_txd <= tx_data[7];4'd9:uart_txd <= 1'b1;default:;endcaseendelserxdata <= 8'd0;endendmoduleendmodule

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