time_counter.vhd

来自「design compile synthesis user guide」· VHDL 代码 · 共 66 行

entity TIME_COUNTER is
    port (HOURS, MINS, SECS, CLK : in BIT;
	  HOURS_OUT : buffer INTEGER range 0 to 12 := 12 ;
	  MINUTES_OUT : buffer INTEGER range 0 to 59 := 0;
	  AM_PM_OUT: buffer BIT := '0');
end;

architecture BEHAVIOR of TIME_COUNTER is

   signal  CURRENT_SECS : INTEGER range 0 to 59;

begin

   process 
   begin
     wait until CLK'event and CLK = '1';

	HOURS_OUT <= HOURS_OUT;
	AM_PM_OUT <= AM_PM_OUT;
	MINUTES_OUT <= MINUTES_OUT;
	CURRENT_SECS <= CURRENT_SECS;

	if (SECS = '1' and MINS = '0' and HOURS = '0') then
	   if CURRENT_SECS = 59 then
	      CURRENT_SECS <= 0;
	      if MINUTES_OUT = 59 then
		 MINUTES_OUT <= 0;
		 if HOURS_OUT = 12 then
		    HOURS_OUT <= 1;
		    AM_PM_OUT <= not AM_PM_OUT;
		 else
		    HOURS_OUT <= HOURS_OUT + 1;
		 end if;
	      else
		 MINUTES_OUT <= MINUTES_OUT + 1;
	      end if;
	   else
	      CURRENT_SECS <= CURRENT_SECS + 1;
	   end if;
	elsif (SECS = '0' and MINS = '1' and HOURS = '0') then
	   CURRENT_SECS <= 0;
	   if MINUTES_OUT = 59 then
	      MINUTES_OUT <= 0;
	      if HOURS_OUT = 12 then
		 HOURS_OUT <= 1;
		 AM_PM_OUT <= not AM_PM_OUT;
	      else
		 HOURS_OUT <= HOURS_OUT + 1;
	      end if;
	   else
	      MINUTES_OUT <= MINUTES_OUT + 1;
	   end if;
	elsif (SECS = '0' and MINS = '0' and HOURS = '1') then
	   CURRENT_SECS <= 0;	
	   if HOURS_OUT = 12 then
	      HOURS_OUT <= 1;
	      AM_PM_OUT <= not AM_PM_OUT;
	   else
	      HOURS_OUT <= HOURS_OUT + 1;
	   end if;
	end if;
	   
   end process;

end BEHAVIOR;