cnt4b.vhd

基于VHDL的4位带异步清零的二进制计数器。

LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;
USE IEEE.STD_LOGIC_UNSIGNED.ALL;
ENTITY CNT4B IS
    PORT (CLK : IN STD_LOGIC;                    
          RST : IN STD_LOGIC;                    
          ENA : IN STD_LOGIC;                     
          OUTY : OUT STD_LOGIC_VECTOR(3 DOWNTO 0);
         COUT : OUT STD_LOGIC    );          
   END CNT4B;
ARCHITECTURE behav OF CNT4B IS
    SIGNAL CQI : STD_LOGIC_VECTOR(3 DOWNTO 0);
BEGIN
P_REG: PROCESS(CLK, RST, ENA)
        BEGIN
         IF RST = '1' THEN   CQI <= "0000";  
           ELSIF CLK'EVENT AND CLK = '1' THEN
             IF ENA = '1' THEN  CQI <= CQI + 1;
           END IF;
         END IF;
		OUTY <= CQI ;
		COUT <= CQI(0) AND CQI(3);--进位输出
		IF CQI = "1010" THEN CQI <= "0000";
        END IF ;
        END PROCESS P_REG ; 
END  behav;