counter.vhd

四位十进制频率计的源代码,详细,清楚地写出了设计语句

LIBRARY IEEE;  
USE IEEE.STD_LOGIC_1164.ALL;
USE IEEE.STD_LOGIC_UNSIGNED.ALL;
ENTITY COUNTER IS
   PORT (FIN : IN STD_LOGIC;                      
          CLR : IN STD_LOGIC;                           
        ENABL : IN STD_LOGIC;                        
        DOUT1,DOUT2,DOUT3,DOUT4 :  OUT STD_LOGIC_VECTOR(3 DOWNTO 0));                                                                         
          END COUNTER;
ARCHITECTURE behav OF COUNTER IS
    SIGNAL c1:STD_LOGIC;
    SIGNAL c2:STD_LOGIC;
    SIGNAL c3:STD_LOGIC;
    SIGNAL c4:STD_LOGIC;
BEGIN
    a:PROCESS(FIN, CLR, ENABL)
variable w1:STD_LOGIC_VECTOR(3 DOWNTO 0);
      BEGIN
        IF CLR = '1' THEN   w1 :=(OTHERS=>'0');    
        ELSIF FIN'EVENT AND FIN = '1' THEN
            IF ENABL = '1' THEN 
         if w1<9  then  w1 :=w1+ 1;
else  w1 :=(OTHERS=>'0');  
  END IF;
 END IF;
   END IF;
if w1=9  then  c1<='1';
else  c1<='0';
end if;
DOUT1(3 DOWNTO 0)<=w1(3 DOWNTO 0 );
    END PROCESS a;
b:PROCESS(c1, clr, ENABL)
variable w2:STD_LOGIC_VECTOR(3 DOWNTO 0);
      BEGIN
        IF CLR = '1' THEN   w2:=(OTHERS=>'0');    
        ELSIF c1'EVENT AND c1 = '0' THEN
            IF ENABL = '1' THEN 
         if w2<9  then  w2 := w2 + 1;
else w2:=(OTHERS=>'0'); 
  END IF;
 END IF;
   END IF;
if w2=9 then  c2<='1';
else  c2<='0';
end if;
DOUT2(3 DOWNTO 0)<=w2(3 DOWNTO 0);
    END PROCESS b;
c:PROCESS(c2, clr, ENABL)
variable w3:STD_LOGIC_VECTOR(3 DOWNTO 0);
      BEGIN
        IF CLR = '1' THEN   w3:=(OTHERS=>'0');    
        ELSIF c2'EVENT AND c2 = '0' THEN
            IF ENABL = '1' THEN 
         if w3<9  then  w3 := w3 + 1;
else w3:=(others=>'0');
  END IF;
 END IF;
   END IF;
if w3=9 then  c3<='1';
else  c3<='0';
end if;
DOUT3(3 DOWNTO 0)<=w3(3 DOWNTO 0 );
    END PROCESS c;
d:PROCESS(c3, clr, ENABL)
variable w4:STD_LOGIC_VECTOR(3 DOWNTO 0);
      BEGIN
        IF CLR = '1' THEN  w4:= (OTHERS=>'0');    
        ELSIF c3'EVENT AND c3 = '0' THEN
            IF ENABL = '1' THEN 
         if w4<9  then  w4 := w4 + 1;
else w4:=(others=>'0');
  END IF;
 END IF;
   END IF;
if w4=9 then  c4<='1';
else  c4<='0';
end if;
DOUT4(3 DOWNTO 0)<=w4(3 DOWNTO 0 );
    END PROCESS d;
END behav;