VHDL设计的串口通信程序

本模块的功能是验证实现和PC机进行基本的串口通信的功能。需要在PC机上安装一个串口调试工具来验证程序的功能。程序实现了一个收发一帧10个bit（即无奇偶校验位）的串口控制器，10个bit是1位起始位，8个数据位，1个结束位。串口的波特律由程序中定义的div_par参数决定，更改该参数可以实现相应的波特率。程序当前设定的div_par 的值是0x104，对应的波特率是9600。用一个8倍波特率的时钟将发送或接受每一位bit的周期时间划分为8个时隙以使通信同步。

　　程序的工作过程是：串口处于全双工工作状态，按动key2，CPLD向PC发送皐elcome字符串（串口调试工具设成按ASCII码接受方式）；PC可随时向CPLD发送0-F的十六进制数据，CPLD接受后显示在7段数码管上。

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;

ENTITY UART IS
PORT (
clk : IN std_logic;
rst : IN std_logic;
rxd : IN std_logic; 串行数据接收端
txd : OUT std_logic; 串行数据发送端
en : OUT std_logic_vector(7 downto 0); 数码管使能
seg_data : OUT std_logic_vector(7 DOWNTO 0); 数码管数据
key_input : IN std_logic 按键输入
);
END UART;

ARCHITECTURE arch OF UART IS
//////////////////inner reg////////////////////
SIGNAL div_reg : std_logic_vector(15 DOWNTO 0);分频计数器，分频值由波特率决定。分频后得到频率8倍波特率的时钟
SIGNAL div8_tras_reg : std_logic_vector(2 DOWNTO 0);该寄存器的计数值对应发送时当前位于的时隙数
SIGNAL div8_rec_reg : std_logic_vector(2 DOWNTO 0); 寄存器的计数值对应接收时当前位于的时隙数
SIGNAL state_tras : std_logic_vector(3 DOWNTO 0); 发送状态寄存器
SIGNAL state_rec : std_logic_vector(3 DOWNTO 0); 接受状态寄存器
SIGNAL clkbaud_tras : std_logic; 以波特率为频率的发送使能信号
SIGNAL clkbaud_rec : std_logic; 以波特率为频率的接受使能信号
SIGNAL clkbaud8x : std_logic; 以8倍波特率为频率的时钟，它的作用是将发送或接受一个bit的时钟周期分为8个时隙
SIGNAL recstart : std_logic; 开始发送标志
SIGNAL recstart_tmp : std_logic; 开始接受标志
SIGNAL trasstart : std_logic;
SIGNAL rxd_reg1 : std_logic; 接收寄存器1
SIGNAL rxd_reg2 : std_logic; 接收寄存器2，因为接收数据为异步信号，故用两级缓存
SIGNAL txd_reg : std_logic; 发送寄存器
SIGNAL rxd_buf : std_logic_vector(7 DOWNTO 0);接受数据缓存
SIGNAL txd_buf : std_logic_vector(7 DOWNTO 0);发送数据缓存
SIGNAL send_state : std_logic_vector(2 DOWNTO 0);每次按键给PC发送Welcome字符串，这是发送状态寄存器
SIGNAL cnt_delay : std_logic_vector(19 DOWNTO 0);延时去抖计数器
SIGNAL start_delaycnt : std_logic; 开始延时计数标志
SIGNAL key_entry1 : std_logic; 确定有键按下曛?
SIGNAL key_entry2 : std_logic; 确定有键按下标志
//////////////////////////////////////////////
C*TANT div_par : std_logic_vector(15 DOWNTO 0) := 0000000100000100;
分频参数，其值由对应的波特率计算而得，按此参数分频的时钟频率是波倍特率的8倍，此处值对应9600的波特率，即分频出的时钟频率是9600*8
SIGNAL txd_xhdl3 : std_logic;

BEGIN
en =01010101 ;7段数码管使能信号赋值
txd = txd_xhdl3;
txd_xhdl3 = txd_reg ;

PROCESS(clk,rst)
BEGIN

IF (NOT rst = ’1’) THEN
cnt_delay = 00000000000000000000;
start_delaycnt = ’0’;
ELSIF(clk’EVENT AND clk=’1’)THEN
IF (start_delaycnt = ’1’) THEN
IF (cnt_delay /= 11000011010100000000) THEN
cnt_delay = cnt_delay + 00000000000000000001;
ELSE
cnt_delay = 00000000000000000000;
start_delaycnt = ’0’;
END IF;
ELSE
IF ((NOT key_input=’1’) AND (cnt_delay = 00000000000000000000)) THEN
start_delaycnt = ’1’;
END IF;
END IF;
END IF;
END PROCESS;

PROCESS(clk,rst)
BEGIN

IF (NOT rst = ’1’) THEN
key_entry1 = ’0’;
ELSIF(clk’EVENT AND clk=’1’)THEN
IF (key_entry2 = ’1’) THEN
key_entry1 = ’0’;
ELSE
IF (cnt_delay = 11000011010100000000) THEN
IF (NOT key_input = ’1’) THEN
key_entry1 = ’1’;
END IF;
END IF;
END IF;
END IF;
END PROCESS;

PROCESS(clk,rst)
BEGIN

IF (NOT rst = ’1’) THEN
div_reg = 0000000000000000;
ELSIF(clk’EVENT AND clk=’1’)THEN
IF (div_reg = div_par - 0000000000000001) THEN
div_reg = 0000000000000000;
ELSE
div_reg = div_reg + 0000000000000001;
END IF;
END IF;
END PROCESS;

PROCESS(clk,rst) 分频得到8倍波特率的时钟
BEGIN

IF (NOT rst = ’1’) THEN
clkbaud8x = ’0’;
ELSIF(clk’EVENT AND clk=’1’)THEN
IF (div_reg = div_par - 0000000000000001) THEN
clkbaud8x = NOT clkbaud8x;
END IF;
END IF;
END PROCESS;

PROCESS(clkbaud8x,rst)
BEGIN
IF (NOT rst = ’1’) THEN
div8_rec_reg = 000;
ELSE IF(clkbaud8x’EVENT AND clkbaud8x = ’1’) THEN
IF (recstart = ’1’) THEN 接收开始标志
div8_rec_reg = div8_rec_reg + 001;接收开始后，时隙数在8倍波特率的时钟下加1循环
END IF;
END IF;
END IF;
END PROCESS;

PROCESS(clkbaud8x,rst)
BEGIN
IF (NOT rst = ’1’) THEN
div8_tras_reg = 000;
ELSE IF(clkbaud8x’EVENT AND clkbaud8x = ’1’) THEN
IF (trasstart = ’1’) THEN
div8_tras_reg = div8_tras_reg + 001;发送开始后，时隙数在8倍波特率的时钟下加1循环
END IF;
END IF;
END IF;
END PROCESS;

PROCESS(div8_rec_reg)
BEGIN
IF (div8_rec_reg = 111) THEN
clkbaud_rec = ’1’; -在第7个时隙，接收
ELSE
clkbaud_rec = ’0’;
END IF;
END PROCESS;

PROCESS(div8_tras_reg)
BEGIN
IF (div8_tras_reg = 111) THEN
clkbaud_tras = ’1’; 在第7个时隙，发送使能信号有效，将数据发出
ELSE
clkbaud_tras = ’0’;
END IF;
END PROCESS;

PROCESS(clkbaud8x,rst)
BEGIN
IF (NOT rst = ’1’) THEN
txd_reg = ’1’;
trasstart = ’0’;
txd_buf = 00000000;
state_tras = 0000;
send_state = 000;
key_entry2 = ’0’;
ELSE IF(clkbaud8x’EVENT AND clkbaud8x = ’1’) THEN
IF (NOT key_entry2 = ’1’) THEN
IF (key_entry1 = ’1’) THEN
key_entry2 = ’1’;
txd_buf = 01110111; w
END IF;
ELSE
CASE state_tras IS
WHEN 0000 => 发送起始位
IF ((NOT trasstart=’1’) AND (send_state 111) ) THEN
trasstart = ’1’;
ELSE
IF (send_state 111) THEN
IF (clkbaud_tras = ’1’) THEN
txd_reg = ’0’;
state_tras = state_tras + 0001;
END IF;
ELSE
key_entry2 = ’0’;
state_tras = 0000;
END IF;
END IF;
WHEN 0001 => 发送第1位
IF (clkbaud_tras = ’1’) THEN
txd_reg = txd_buf(0);
txd_buf(6 DOWNTO 0) = txd_buf(7 DOWNTO 1);
state_tras = state_tras + 0001;
END IF;
WHEN 0010 => 发送第2位
IF (clkbaud_tras = ’1’) THEN
txd_reg = txd_buf(0);
txd_buf(6 DOWNTO 0) = txd_buf(7 DOWNTO 1);
state_tras = state_tras + 0001;
END IF;
WHEN 0011 => 发送第3位
IF (clkbaud_tras = ’1’) THEN
txd_reg = txd_buf(0);
txd_buf(6 DOWNTO 0) = txd_buf(7 DOWNTO 1);
state_tras = state_tras + 0001;
END IF;
WHEN 0100 => 发送第4位
IF (clkbaud_tras = ’1’) THEN
txd_reg = txd_buf(0);
txd_buf(6 DOWNTO 0) = txd_buf(7 DOWNTO 1);
state_tras = state_tras + 0001;
END IF;
WHEN 0101 => 发送第5位
IF (clkbaud_tras = ’1’) THEN
txd_reg = txd_buf(0);
txd_buf(6 DOWNTO 0) = txd_buf(7 DOWNTO 1);
state_tras = state_tras + 0001;
END IF;
WHEN 0110 => 发送第6位
IF (clkbaud_tras = ’1’) THEN
txd_reg = txd_buf(0);
txd_buf(6 DOWNTO 0) = txd_buf(7 DOWNTO 1);
state_tras = state_tras + 0001;
END IF;
WHEN 0111 => 发送第7位
IF (clkbaud_tras = ’1’) THEN
txd_reg = txd_buf(0);
txd_buf(6 DOWNTO 0) = txd_buf(7 DOWNTO 1);
state_tras = state_tras + 0001;
END IF;
WHEN 1000 => 发送第8位
IF (clkbaud_tras = ’1’) THEN
txd_reg = txd_buf(0);
txd_buf(6 DOWNTO 0) = txd_buf(7 DOWNTO 1);
state_tras = state_tras + 0001;
END IF;
WHEN 1001 => 发送停止位
IF (clkbaud_tras = ’1’) THEN
txd_reg = ’1’;
txd_buf = 01010101;
state_tras = state_tras + 0001;
END IF;
WHEN 1111 =>
IF (clkbaud_tras = ’1’) THEN
state_tras = state_tras + 0001;
send_state = send_state + 001;
trasstart = ’0’;
CASE send_state IS
WHEN 000 =>
txd_buf = 01100101; e
WHEN 001 =>
txd_buf = 01101100; l
WHEN 010 =>
txd_buf = 01100011; c
WHEN 011 =>
txd_buf = 01101111; o
WHEN 100 =>
txd_buf = 01101101; m
WHEN 101 =>
txd_buf = 01100101; e
WHEN OTHERS =>
txd_buf = 00000000;

END CASE;
END IF;
WHEN OTHERS =>
IF (clkbaud_tras = ’1’) THEN
state_tras = state_tras + 0001;
trasstart = ’1’;
END IF;

END CASE;
END IF;
END IF;
END IF;
END PROCESS;

PROCESS(clkbaud8x,rst) 接受PC机的数据
BEGIN
IF (NOT rst = ’1’) THEN
rxd_reg1 = ’0’;
rxd_reg2 = ’0’;
rxd_buf = 00000000;
state_rec = 0000;
recstart = ’0’;
recstart_tmp = ’0’;
ELSE IF(clkbaud8x’EVENT AND clkbaud8x = ’1’) THEN
rxd_reg1 = rxd;
rxd_reg2 = rxd_reg1;
IF (state_rec = 0000) THEN
IF (recstart_tmp = ’1’) THEN
recstart = ’1’;
recstart_tmp = ’0’;
state_rec = state_rec + 0001;
ELSE
IF ((NOT rxd_reg1 AND rxd_reg2) = ’1’) THEN 检测到起始位的下降沿，进入接受状态
recstart_tmp = ’1’;
END IF;
END IF;
ELSE
IF (state_rec >= 0001 AND state_rec=1000) THEN
IF (clkbaud_rec = ’1’) THEN
rxd_buf(7) = rxd_reg2;
rxd_buf(6 DOWNTO 0) = rxd_buf(7 DOWNTO 1);
state_rec = state_rec + 0001;
END IF;
ELSE
IF (state_rec = 1001) THEN
IF (clkbaud_rec = ’1’) THEN
state_rec = 0000;
recstart = ’0’;
END IF;
END IF;
END IF;
END IF;
END IF;
END IF;
END PROCESS;

PROCESS(rxd_buf) 将接受的数据用数码管显示出来
BEGIN
CASE rxd_buf IS
WHEN 00110000 =>
seg_data = 00000011; 0
WHEN 00110001 =>
seg_data = 10011111; 1
WHEN 00110010 =>
seg_data = 00100101; 2
WHEN 00110011 =>
seg_data = 00001101; 3
WHEN 00110100 =>
seg_data = 10011001; 4
nbs p; WHEN 00110101 =>
seg_data = 01001001; 5
WHEN 00110110 =>
seg_data = 01000001; 6
WHEN 00110111 =>
seg_data = 00011111; 7
WHEN 00111000 =>
seg_data = 00000001; 8
WHEN 00111001 =>
seg_data = 00001001; 9
WHEN 01000001 =>
seg_data = 00010001; A
WHEN 01000010 =>
seg_data = 11000001; B
WHEN 01000011 =>
seg_data = 01100011; C
WHEN 01000100 =>
seg_data = 10000101; D
WHEN 01000101 =>
seg_data = 01100001; E
WHEN 01000110 =>
seg_data = 01110001; F
WHEN OTHERS =>
seg_data = 11111111;
END CASE;
END PROCESS;
END arch;