-- MAX+plus II VHDL Example
-- Efficient Counter Inference
-- Copyright (c) 1994 Altera Corporation
-- download from:www.pld.com.cn & www.fpga.com.cn

Library IEEE ;
use IEEE.std_logic_1164.all ;
use IEEE.std_logic_arith.all ;

ENTITY counters IS

	PORT
	(
		d		: IN 	INTEGER RANGE 0 TO 255;
		clk		: IN	BIT;
		clear	: IN	BIT;
		ld		: IN	BIT;
		enable	: IN	BIT;
		up_down	: IN	BIT;
		qa		: OUT 	INTEGER RANGE 0 TO 255;
		qb		: OUT 	INTEGER RANGE 0 TO 255;
		qc		: OUT 	INTEGER RANGE 0 TO 255;
		qd		: OUT 	INTEGER RANGE 0 TO 255;
		qe		: OUT 	INTEGER RANGE 0 TO 255;
		qf		: OUT 	INTEGER RANGE 0 TO 255;
		qg		: OUT 	INTEGER RANGE 0 TO 255;
		qh		: OUT 	INTEGER RANGE 0 TO 255;
		qi		: OUT 	INTEGER RANGE 0 TO 255;
		qj		: OUT 	INTEGER RANGE 0 TO 255;
		qk		: OUT 	INTEGER RANGE 0 TO 255;
		ql		: OUT 	INTEGER RANGE 0 TO 255;
		qm		: OUT 	INTEGER RANGE 0 TO 255;
		qn		: OUT 	INTEGER RANGE 0 TO 255
	);
	
END counters;

ARCHITECTURE a OF counters IS
BEGIN
	-- An enable counter
	PROCESS (clk)
		VARIABLE	cnt			: INTEGER RANGE 0 TO 255;
	BEGIN
		IF (clk'EVENT AND clk = '1') THEN
			IF enable = '1' THEN
				cnt := cnt + 1;
			END IF;
		END IF;
		
		qa	<= cnt;

	END PROCESS;

	-- A synchronous load counter
	PROCESS (clk)
		VARIABLE	cnt			: INTEGER RANGE 0 TO 255;
	BEGIN
		IF (clk'EVENT AND clk = '1') THEN
			IF ld = '0' THEN
				cnt := d;
			ELSE
				cnt := cnt + 1;
			END IF;
		END IF;

		qb	<=	cnt;
	END PROCESS;

	-- A synchronous clear counter
	PROCESS (clk)
		VARIABLE	cnt			: INTEGER RANGE 0 TO 255;
	BEGIN
		IF (clk'EVENT AND clk = '1') THEN
			IF clear = '0' THEN
				cnt := 0;
			ELSE
				cnt := cnt + 1;
			END IF;
		END IF;

		qc	<=	cnt;
	
	END PROCESS;

	-- An up/down counter
	PROCESS (clk)
		VARIABLE	cnt			: INTEGER RANGE 0 TO 255;
		VARIABLE	direction 	: INTEGER;
	BEGIN
		IF (up_down = '1') THEN
			direction := 1;
		ELSE
			direction := -1;
		END IF;
		
		IF (clk'EVENT AND clk = '1') THEN
			cnt := cnt + direction;
		END IF;

		qd	<=	cnt;
	
	END PROCESS;

	-- A synchronous load enable counter
	PROCESS (clk)
		VARIABLE	cnt			: INTEGER RANGE 0 TO 255;
	BEGIN
		IF (clk'EVENT AND clk = '1') THEN
			IF ld = '0' THEN
				cnt := d;
			ELSE
				IF enable = '1' THEN
					cnt := cnt + 1;
				END IF;
			END IF;
		END IF;

		qe	<=	cnt;
	
	END PROCESS;

	-- An enable up/down counter
	PROCESS (clk)
		VARIABLE	cnt			: INTEGER RANGE 0 TO 255;
		VARIABLE	direction 	: INTEGER;
	BEGIN
		IF (up_down = '1') THEN
			direction := 1;
		ELSE
			direction := -1;
		END IF;
		
		IF (clk'EVENT AND clk = '1') THEN
			IF enable = '1' THEN
				cnt := cnt + direction;
			END IF;
		END IF;

		qf	<=	cnt;
	
	END PROCESS;

	-- A synchronous clear enable counter
	PROCESS (clk)
		VARIABLE	cnt			: INTEGER RANGE 0 TO 255;
	BEGIN
		IF (clk'EVENT AND clk = '1') THEN
			IF clear = '0' THEN
				cnt := 0;
			ELSE
				IF enable = '1' THEN
					cnt := cnt + 1;
				END IF;
			END IF;
		END IF;

		qg	<=	cnt;
	
	END PROCESS;

	-- A synchronous load clear counter
	PROCESS (clk)
		VARIABLE	cnt			: INTEGER RANGE 0 TO 255;
	BEGIN
		IF (clk'EVENT AND clk = '1') THEN
			IF clear = '0' THEN
				cnt := 0;
			ELSE
				IF ld = '0' THEN
					cnt := d;
				ELSE
					cnt := cnt + 1;
				END IF;
			END IF;
		END IF;

		qh	<=	cnt;
	
	END PROCESS;

	-- A synchronous load up/down counter
	PROCESS (clk)
		VARIABLE	cnt			: INTEGER RANGE 0 TO 255;
		VARIABLE	direction 	: INTEGER;
	BEGIN
		IF (up_down = '1') THEN
			direction := 1;
		ELSE
			direction := -1;
		END IF;
		
		IF (clk'EVENT AND clk = '1') THEN
			IF ld = '0' THEN
				cnt := d;
			ELSE
				cnt := cnt + direction;
			END IF;
		END IF;

		qi	<=	cnt;
	
	END PROCESS;

	-- A synchronous load enable up/down counter
	PROCESS (clk)
		VARIABLE	cnt			: INTEGER RANGE 0 TO 255;
		VARIABLE	direction 	: INTEGER;
	BEGIN
		IF (up_down = '1') THEN
			direction := 1;
		ELSE
			direction := -1;
		END IF;
		
		IF (clk'EVENT AND clk = '1') THEN
			IF ld = '0' THEN
				cnt := d;
			ELSE
				IF enable = '1' THEN
					cnt := cnt + direction;
				END IF;
			END IF;
		END IF;

		qj	<=	cnt;

	END PROCESS;

	-- A synchronous clear load enable counter
	PROCESS (clk)
		VARIABLE	cnt			: INTEGER RANGE 0 TO 255;
	BEGIN
		IF (clk'EVENT AND clk = '1') THEN
			IF clear = '0' THEN
				cnt := 0;
			ELSE
				IF ld = '0' THEN
					cnt := d;
				ELSE
					IF enable = '1' THEN
						cnt := cnt + 1;
					END IF;
				END IF;
			END IF;
		END IF;
		
		qk	<=	cnt;
	
	END PROCESS;

	-- A synchronous clear up/down counter
	PROCESS (clk)
		VARIABLE	cnt			: INTEGER RANGE 0 TO 255;
		VARIABLE	direction 	: INTEGER;
	BEGIN
		IF (up_down = '1') THEN
			direction := 1;
		ELSE
			direction := -1;
		END IF;
		
		IF (clk'EVENT AND clk = '1') THEN
			IF clear = '0' THEN
				cnt := 0;
			ELSE
				cnt := cnt + direction;
			END IF;
		END IF;

		ql	<=	cnt;
	
	END PROCESS;

	-- A synchronous clear enable up/down counter
	PROCESS (clk)
		VARIABLE	cnt			: INTEGER RANGE 0 TO 255;
		VARIABLE	direction 	: INTEGER;
	BEGIN
		IF (up_down = '1') THEN
			direction := 1;
		ELSE
			direction := -1;
		END IF;
		
		IF (clk'EVENT AND clk = '1') THEN
			IF clear = '0' THEN
				cnt := 0;
			ELSE
				IF enable = '1' THEN
					cnt := cnt + direction;
				END IF;
			END IF;
		END IF;

		qm	<=	cnt;
	
	END PROCESS;

	-- A modulus 200 up counter
	PROCESS (clk)
		VARIABLE	cnt			: INTEGER RANGE 0 TO 255;
		CONSTANT	modulus 	: INTEGER := 200;
	BEGIN
		IF (clk'EVENT AND clk = '1') THEN
			IF cnt = modulus THEN
				cnt := 0;
			ELSE
				cnt := cnt + 1;
			END IF;
		END IF;

		qn	<=	cnt;
	
	END PROCESS;
END a;