taxi.vhd

出租车计价器的计路程模块的源代码

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_arith.all;
use ieee.std_logic_unsigned.all;


entity taxi  is
	port (  
	  clk,reset:in std_logic;--每来一个脉冲（代表运行了0.1公里)
	  en1:out std_logic;                    --超出起车里程开始记价使能信号（7元)
      count1 :out std_logic_vector (3 downto 0);--――里程数值的十分位
      count2 :out std_logic_vector (3 downto 0); --――里程数值的个位
      count3 :out std_logic_vector (3 downto 0)); --――里程数值的十位
end taxi ;


architecture aa of taxi is
begin
  process(clk,reset)
	variable mm : std_logic_vector (11 downto 0);
begin
	if reset='1' then
	  mm:="000000000000";
	elsif clk'event and clk='1' then
        if mm(3 downto 0)="1001" then--――十六进制转换成十进制
			 mm:=mm+7;
		else 
		     mm:=mm+1; 
		end if;
		if mm(7 downto 4)="1010" then
			mm:=mm+"01100000"; 
		end if;
	end if; 
	if mm(11 downto 4)>"00000111" then 
      en1<='1';
	else 
	    en1<='0';
	end if;
count1<=mm(3 downto 0);
count2<=mm(7 downto 4);
count3<=mm(11 downto 8);
end process;
end aa;