计数器：generic语句的应用.txt

很好的VHDL源码,里面有不少实用的实例!

-- n-Bit Synchronous Counter
-- dowload from: www.fpga.com.cn & www.pld.com.cn

LIBRARY ieee;
USE ieee.Std_logic_1164.ALL;
USE ieee.Std_logic_unsigned.ALL;

ENTITY cntrnbit IS
        GENERIC(n : Positive := 8);
        PORT(clock, reset, enable : IN Std_logic; 
             count : OUT Std_logic_vector((n-1) DOWNTO 0));
END cntrnbit;

ARCHITECTURE v1 OF cntrnbit IS
        SIGNAL count_int : Std_logic_vector((n-1) DOWNTO 0);
BEGIN

        PROCESS
        BEGIN
                WAIT UNTIL rising_edge(clock);
                IF reset = '1' THEN 
                        count_int <= (OTHERS => '0');
                ELSIF enable = '1' THEN
                        count_int <= count_int + 1;
                ELSE
                        NULL;
                END IF;
        END PROCESS;
        count <= count_int;
END v1;