upcnt5.vhd

spi总线的vhdl代码

-- File:     upcnt5.vhd
-- 
-- Purpose:  Up 5-bit counter
--
-- Created:  7-25-00 ALS
--
	


library IEEE;
use IEEE.std_logic_1164.all;
use IEEE.std_logic_arith.all;


entity upcnt5 is
	port(
	      
	     cnt_en       : in STD_LOGIC;                        -- Count enable                       -- Load line enable
 	     clr          : in STD_LOGIC;                        -- Active low clear
	     clk          : in STD_LOGIC;                        -- Clock
	     qout         : inout STD_LOGIC_VECTOR (4 downto 0)
		
	     );
		
end upcnt5;


architecture DEFINITION of upcnt5 is

constant RESET_ACTIVE : std_logic := '0';

signal q_int : UNSIGNED (4 downto 0);

begin

     process(clk, clr)
     begin
          
          -- Clear output register
          if (clr = RESET_ACTIVE) then
	       q_int <= (others => '0');
	       
	  -- On rising edge of clock count
	  elsif (clk'event) and clk = '1' then
	       if cnt_en = '1' then
		    	q_int <= q_int + 1;
	       end if;
	  end if;

     end process;

     qout <= STD_LOGIC_VECTOR(q_int);

end DEFINITION;