counter24b.vhd

可编程逻辑设计的程序！24位十进制频率计！可使ＥＤＡ实验年箱测量指定频率！

LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;
USE IEEE.STD_LOGIC_UNSIGNED.ALL;
ENTITY COUNTER24B IS
   PORT(FIN: IN STD_LOGIC;
        CLR: IN STD_LOGIC;
        ENABL: IN STD_LOGIC;
        COUT:OUT STD_LOGIC;
        DOUT:OUT STD_LOGIC_VECTOR(23 DOWNTO 0));
END COUNTER24B;
ARCHITECTURE behav OF COUNTER24B IS
SIGNAL Q0,Q1,Q2,Q3,Q4,Q5: STD_LOGIC_VECTOR(3 DOWNTO 0);
SIGNAL C0,C1,C2,C3,C4,C5: STD_LOGIC;
BEGIN
PROCESS(FIN,ENABL,CLR)
  BEGIN
  IF CLR='1' THEN Q0<=(OTHERS=>'0');Q1<=(OTHERS=>'0');Q2<=(OTHERS=>'0');Q3<=(OTHERS=>'0');Q4<=(OTHERS=>'0');Q5<=(OTHERS=>'0');C5<='0';
     ELSIF FIN'EVENT AND FIN='1' THEN
     IF ENABL='1' THEN 
        IF Q0<"1001" THEN Q0<=Q0+1;
        elsif Q0>"1001" THEN Q0<=(OTHERS=>'0');
         elsif
           Q0="1001" THEN  C0<='1';Q0<=(OTHERS=>'0'); 
            IF Q1<"1001" THEN Q1<=Q1+1;
                elsif Q1>"1001" THEN Q1<=(OTHERS=>'0');
              elsif Q1="1001" THEN   C1<='1';Q1<=(OTHERS=>'0');
                IF Q2<"1001" THEN Q2<=Q2+1;
                  elsif Q2>"1001" THEN Q2<=(OTHERS=>'0');
                  elsif Q2="1001" THEN   C2<='1';Q2<=(OTHERS=>'0');
                    IF Q3<"1001" THEN Q3<=Q3+1;
                       elsif Q3>"1001" THEN Q3<=(OTHERS=>'0');
                       elsif Q3="1001" THEN   C3<='1';Q3<=(OTHERS=>'0');
                          IF Q4<"1001" THEN Q4<=Q4+1;
                             elsif Q4>"1001" THEN Q4<=(OTHERS=>'0');
                             elsif Q4="1001" THEN   C4<='1';Q4<=(OTHERS=>'0');
                                IF Q5<"1001" THEN Q5<=Q5+1;
                                   elsif Q5>="1001" THEN   C5<='1';Q5<=(OTHERS=>'0');
                                   ELSE C5<='0';                                   
                                END IF;
                             ELSE C4<='0';
                             END IF;
                           ELSE C3<='0';
                         END IF;
                  ELSE C2<='0';
                  END IF;
              ELSE C1<='0';
            END IF;
          ELSE C0<='0';
        END IF;
      END IF;
   END IF;
END PROCESS;
COUT<=C5;
DOUT<=Q5&Q4&Q3&Q2&Q1&Q0;
END behav;