说明：  已经验证过的I2C，slave的IP，core，从一开源网站下载的，代码写的非常好，节省了FPGA的资源，比起以往的slave的CORE，这个CORE减少了寄存器的使用。
(Has been verified I2C, slave of the IP, core, from an open source website, the code is written in a very good save FPGA resources than the previous slave of CORE, the CORE reduce the use of registers.)