VHDL設計的串口通信程序
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本模塊的功能是驗證實現和PC機進行基本的串口通信的功能。需要在PC機上安裝一個串口調試工具來驗證程序的功能。程序實現了一個收發(fā)一幀10個bit（即無奇偶校驗位）的串口控制器，10個bit是1位起始位，8個數據位，1個結束位。串口的波特律由程序中定義的div_par參數決定，更改該參數可以實現相應的波特率。程序當前設定的div_par 的值是0x104，對應的波特率是9600。用一個8倍波特率的時鐘將發(fā)送或接受每一位bit的周期時間劃分為8個時隙以使通信同步。
本文引用地址：http://www.czjhyjcfj.com/article/201706/349336.htm程序的工作過程是：串口處于全雙工工作狀態(tài)，按動key2，CPLD向PC發(fā)送皐elcome字符串（串口調試工具設成按ASCII碼接受方式）；PC可隨時向CPLD發(fā)送0-F的十六進制數據，CPLD接受后顯示在7段數碼管上。
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; 串行數據接收端
txd : OUT std_logic; 串行數據發(fā)送端
en : OUT std_logic_vector(7 downto 0); 數碼管使能
seg_data : OUT std_logic_vector(7 DOWNTO 0); 數碼管數據
key_input : IN std_logic 按鍵輸入
);
END UART;
ARCHITECTURE arch OF UART IS
//////////////////inner reg////////////////////
SIGNAL div_reg : std_logic_vector(15 DOWNTO 0);分頻計數器，分頻值由波特率決定。分頻后得到頻率8倍波特率的時鐘
SIGNAL div8_tras_reg : std_logic_vector(2 DOWNTO 0);該寄存器的計數值對應發(fā)送時當前位于的時隙數
SIGNAL div8_rec_reg : std_logic_vector(2 DOWNTO 0); 寄存器的計數值對應接收時當前位于的時隙數
SIGNAL state_tras : std_logic_vector(3 DOWNTO 0); 發(fā)送狀態(tài)寄存器
SIGNAL state_rec : std_logic_vector(3 DOWNTO 0); 接受狀態(tài)寄存器
SIGNAL clkbaud_tras : std_logic; 以波特率為頻率的發(fā)送使能信號
SIGNAL clkbaud_rec : std_logic; 以波特率為頻率的接受使能信號
SIGNAL clkbaud8x : std_logic; 以8倍波特率為頻率的時鐘，它的作用是將發(fā)送或接受一個bit的時鐘周期分為8個時隙
SIGNAL recstart : std_logic; 開始發(fā)送標志
SIGNAL recstart_tmp : std_logic; 開始接受標志
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，因為接收數據為異步信號，故用兩級緩存
SIGNAL txd_reg : std_logic; 發(fā)送寄存器
SIGNAL rxd_buf : std_logic_vector(7 DOWNTO 0);接受數據緩存
SIGNAL txd_buf : std_logic_vector(7 DOWNTO 0);發(fā)送數據緩存
SIGNAL send_state : std_logic_vector(2 DOWNTO 0);每次按鍵給PC發(fā)送Welcome字符串，這是發(fā)送狀態(tài)寄存器
SIGNAL cnt_delay : std_logic_vector(19 DOWNTO 0);延時去抖計數器
SIGNAL start_delaycnt : std_logic; 開始延時計數標志
SIGNAL key_entry1 : std_logic; 確定有鍵按下曛?
SIGNAL key_entry2 : std_logic; 確定有鍵按下標志
//////////////////////////////////////////////
C*TANT div_par : std_logic_vector(15 DOWNTO 0) := 0000000100000100;
分頻參數，其值由對應的波特率計算而得，按此參數分頻的時鐘頻率是波倍特率的8倍，此處值對應9600的波特率，即分頻出的時鐘頻率是9600*8
SIGNAL txd_xhdl3 : std_logic;
BEGIN
en =01010101 ;7段數碼管使能信號賦值
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) 分頻得到8倍波特率的時鐘
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 接收開始標志
div8_rec_reg = div8_rec_reg + 001;接收開始后，時隙數在8倍波特率的時鐘下加1循環(huán)
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;發(fā)送開始后，時隙數在8倍波特率的時鐘下加1循環(huán)
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個時隙，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個時隙，發(fā)送使能信號有效，將數據發(fā)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 => 發(fā)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 => 發(fā)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 => 發(fā)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 => 發(fā)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 => 發(fā)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 => 發(fā)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 => 發(fā)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 => 發(fā)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 => 發(fā)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 => 發(fā)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機的數據
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 檢測到起始位的下降沿，進入接受狀態(tài)
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) 將接受的數據用數碼管顯示出來
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;
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