多位的数据赋值给单位数据的方法很好的解决PWM的问题。
代码如下：
library IEEE;
use IEEE.STD_LOGIC_1164.all;
use IEEE.STD_LOGIC_UNSIGNED.ALL;
entity pwm_test is
port (
clk : in std_logic;
PWM_in : in std_logic_vector (7 downto 0) := "00000000";
PWM_out : out std_logic
);
end pwm_test;
architecture PWM_arch of pwm_test is
signal PWM_Accumulator : std_logic_vector(8 downto 0);
begin
process(clk, PWM_in)
begin
if rising_edge(clk) then
PWM_Accumulator <= ("0" & PWM_Accumulator(7 downto 0)) + ("0" & PWM_in);
end if;
end process;
PWM_out <= PWM_Accumulator(8);
end PWM_arch;
