本程序代码是使用I2C通信的一个例子，主要实现I2C与在读写模式下的PCF8574通信。-I2C communication with a PCF8574 in read and write mode is demonstrated. PCF8574 port P is configured with P0-P3 input, P4-P7. Read P0-P3 input data is written back to Port P4-P7. This example uses t