ADC0809 VHDL控制程序
--文件名：ADC0809.vhd
--功能：基于VHDL語言，實現對ADC0809簡單控制
--說明：ADC0809沒有內部時鐘，需外接10KHz~1290Hz的時鐘信號，這里由FPGA的系
--統時鐘（50MHz）經256分頻得到clk1（195KHz）作為ADC0809轉換工作時鐘。
--最后修改日期：2004.3.20
library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
use ieee.std_logic_arith.all;
entity ADC0809 is
? port (?? d?????? : in std_logic_vector(7 downto 0);????????? --ADC0809輸出的采樣數據
???????? clk,eoc?? : in std_logic;??????? --clk為系統時鐘，eoc為ADC0809轉換結束信號
clk1,start, ale,en: out std_logic;??????????????????????????????? --ADC0809控制信號
??????? abc_in??? :in std_logic_vector(2 downto 0);???????????????????? --模擬選通信號
abc_out???? :out std_logic_vector(2 downto 0);??????? --ADC0809模擬信號選通信號
??????? q??????? : out std_logic_vector(7 downto 0));????????? --送至8個并排數碼管信號
?end ADC0809;
architecture behav of ADC0809 is
type states is ( st0,st1, st2, st3, st4,st5,st6);???????????????????????? --定義各狀態的子類型
signal current_state, next_state:states:=st0;
signal regl :std_logic_vector(7 downto 0);??????????????????????????? --中間數據寄存信號
signal qq:std_logic_vector(7 downto 0);
begin
com:process(current_state,eoc)???????????????????????????? --規定各種狀態的轉換方式
begin
? case current_state is
? when st0=>next_state<=st1;ale<='0';start<='0';en<='0';
? when st1=>next_state<=st2;ale<='1';start<='0';en<='0';
? when st2=>next_state<=st3;ale<='0';start<='1';en<='0';
? when st3=>???????????? ale<='0';start<='0';en<='0';
??????? if eoc='1' then next_state<=st3;??????????????????????????? --檢測EOC的下降沿
??????? else next_state<=st4;
??????? end if;???
? when st4=>????????????? ale<='0';start<='0';en<='0';
??????? if eoc='0' then next_state<=st4;??????????????????????????? --檢測EOC的上升沿
else next_state<=st5;
end if;
? when st5=>next_state<=st6;ale<='0';start<='0';en<='1';
? when st6=>next_state<=st0;ale<='0';start<='0';en<='1';regl<=d;
? when others=> next_state<=st0;ale<='0';start<='0';en<='0';
? end case;
end process;
clock:process(clk)???????????????? --對系統時鐘進行分頻，得到ADC0809轉換工作時鐘
begin
?if clk'event and clk='1' then qq<=qq+1;????????????? --在clk1的上升沿，轉換至下一狀態
if QQ="01111111" THEN clk1<='1'; current_state <=next_state;???
? elsif qq<="01111111" then clk1<='0';?
??? end if;?
end if;
end process;
q<=regl;? abc_out<=abc_in;?
end behav;?

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