cnt8.vhd

一个PWM波的设计实例。弄直流点击的可以认真的学习一下

LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;
USE IEEE.STD_LOGIC_UNSIGNED.ALL;

ENTITY CNT8 IS
    PORT (
        CLK, LD : IN STD_LOGIC;
        D : IN STD_LOGIC_VECTOR(3 DOWNTO 0);
        CAO : OUT STD_LOGIC
    );
END CNT8;

ARCHITECTURE behav OF CNT8 IS
    SIGNAL COUNT : STD_LOGIC_VECTOR(3 DOWNTO 0);
BEGIN
    PROCESS( CLK )
    BEGIN
        IF CLK'EVENT AND CLK = '1' THEN
            IF LD = '1' THEN
                COUNT <= D;
            ELSE
                COUNT <= COUNT - 1;
            END IF;
        END IF;
    END PROCESS;
CAO<='1' WHEN COUNT="0000" ELSE '0';    
   
END behav;