keyboard_scan.vhd

VHDL基础的编程源代码

--/*****************************************************************************
-- * 源文件:	keyboard_scan.vhd
-- * 模块:   	键盘扫描信号发生器
-- * 版权:
-- *         	Copyright(C) 北京联华众科科技有限公司
-- *						www.lianhua-zhongke.com.cn
-- * 版本：  	Version 1.0
-- * 
-- * 功能说明:
-- *		   	与输入时钟 clock 同频率产生键盘扫描信号，键盘扫描信号为低电平有效
-- *			
-- * 参数说明：
-- *	       	输出
-- *			row_select - 键盘行扫描信号，只有一位为低其余位为高电平，属于低
-- *						电平有效
-- *
-- *			输入
-- *			clock - 键盘扫描驱动时钟
-- *			reset - 复位信号，低电平有效
-- *
-- *			参数
-- *			keyboard_size - 键盘扫描数据位数
-- *
-- * 变更记录: 
-- *         2006.01.28, 新建
-- *
-- *****************************************************************************/
LIBRARY ieee;
USE ieee.std_logic_1164.all;
USE ieee.std_logic_arith.all;
USE ieee.std_logic_unsigned.all;

ENTITY keyboard_scan IS
	GENERIC
	(
		keyboard_size : INTEGER RANGE 0 TO 15:= 4
	);
	
	PORT
	(
		row_select : OUT STD_LOGIC_VECTOR(keyboard_size-1 downto 0);

		clock	: IN STD_LOGIC;
		reset 	: IN STD_LOGIC
	);
	
END keyboard_scan;

ARCHITECTURE keyboard_scan_architecture OF keyboard_scan IS	
BEGIN
	
	PROCESS(clock, reset)
		VARIABLE row_counter : INTEGER RANGE 0 TO keyboard_size-1;
	BEGIN		
		IF (reset = '0') THEN
			row_select <= NOT CONV_STD_LOGIC_VECTOR(0, keyboard_size);
			row_counter := 0;
		ELSIF(clock = '1' AND clock'EVENT) THEN
			row_select <= NOT CONV_STD_LOGIC_VECTOR(0, keyboard_size);
			row_select(row_counter) <= '0';
			
			IF (row_counter = keyboard_size-1) THEN
				row_counter := 0;
			ELSE
				row_counter := row_counter+1;
			END IF;
			
		END IF;
		
	END PROCESS;

END keyboard_scan_architecture;