4*4键盘扫描程序，本程序默认键盘总线接到P2端口，并且把P2口的低四位作为X坐标，高四位作为Y坐标。如不是用P2口做键盘总线，修改“KEYBUS”。-4* 4 keypad scanner, the program received a default keyboard bus port P2 and the P2 port four as the X coordinate of the low and high four as the Y coordinates. If it is not done with the keyboard port P2 bus, modified " KEYBUS" .