key_decode.vhd

VHDL基础的编程源代码

--/*****************************************************************************
-- * 源文件:	key_decode.vhd
-- * 模块:   	键盘译码
-- * 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:
-- *		   	将扫描读到的按键 8 位按键码转换为 4 位的按键值。
-- *			
-- * 参数说明：
-- *	       	输出
-- *			key - 4 位的按键值
-- *
-- *			输入
-- *			key_data - 8位按键码
-- *			reset - 复位信号，低电平有效
-- *
-- *			参数
-- *
-- * 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 key_decode IS
	PORT
	(
		key			: OUT	STD_LOGIC_VECTOR(3 DOWNTO 0);
		
		key_data	: IN	STD_LOGIC_VECTOR(7 DOWNTO 0);
		reset		: IN	STD_LOGIC
	);
END key_decode;

ARCHITECTURE key_decode_architecture OF key_decode IS	
BEGIN

	PROCESS(key_data, reset)
	BEGIN		
		IF (reset = '0') THEN
			key <= "0000";
		ELSE
			CASE NOT key_data IS
				WHEN "00010001" => key <= "0000";
				WHEN "00010010" => key <= "0001";
				WHEN "00010100" => key <= "0010";
				WHEN "00011000" => key <= "0011";
				WHEN "00100001" => key <= "0100";
				WHEN "00100010" => key <= "0101";
				WHEN "00100100" => key <= "0110";
				WHEN "00101000" => key <= "0111";
				WHEN "01000001" => key <= "1000";
				WHEN "01000010" => key <= "1001";
				WHEN "01000100" => key <= "1010";
				WHEN "01001000" => key <= "1011";
				WHEN "10000001" => key <= "1100";
				WHEN "10000010" => key <= "1101";
				WHEN "10000100" => key <= "1110";
				WHEN "10001000" => key <= "1111";
				WHEN OTHERS => key <= "0000";
			END CASE;
			
		END IF;
		
	END PROCESS;

END key_decode_architecture;