说明：  //使用说明: //使用前请先定义keyscan为单片机的 //某个端口,如#define keyscan P1 //程序中扫描信号从keyscan高4位输出， //键值返回信号从keyscan低4位读入， //故使用时硬件电路需要与之相对， //或者把软件中相应地方修改即可
(//use :// use the former post keyscan definition of SCM// a port, keyscan such as# define P1// scanning process signals from four keyscan high output// keys to a signal from the four low-keyscan read,// use it when necessary hardware circuit Correspondingly,// or software which can be revised accordingly places)