2.微秒模块
采用VHDL语言输入方式,以时钟clk,清零信号clr以及暂停信号STOP为进程敏感变量,程序如下：
library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
entity MINSECONDb is
port(clk,clrm,stop:in std_logic;----时钟/清零信号
secm1,secm0:out std_logic_vector(3 downto 0);----秒高位/低位
co:out std_logic);-------输出/进位信号
end MINSECONDb;
architecture SEC of MINSECONDb is
signal clk1,DOUT2:std_logic;
begin
process(clk,clrm)
variable cnt1,cnt0:std_logic_vector(3 downto 0);---计数
VARIABLE COUNT2 :INTEGER RANGE 0 TO 10 ;
begin
IF CLK'EVENT AND CLK='1'THEN
IF COUNT2>=0 AND COUNT2