说明：  用51单片机普通io口模拟的i2c总线协议，也是我全国电子设计大赛集训时写的，keil c51编写，一条总线上可以挂接多个器件，多于节省io口很有帮助。
(With 51 single-chip simulation of ordinary io I i2c bus protocol, but also the national electronic design contest I am writing training, keil c51 prepared, a bus can be articulated multiple devices, saving more than helpful io mouth.)