This is some info on how the I2C Protocol works.
Basically SDA is brought low by the master (sender), on the falling edge of the SCL (clock). Then a 7 bit address representing which data address will be accessed. This is then followed by a reading or writing bit that will let you know if the address needs to respond or receive data. HIGH means data will be read, and LOW means data will be written. The slave (receiver), will then respond by pulling the data line down letting the master, it received the info. This is then followed by a byte of data. Then finally one more ACK (acknowledged) bit sent by the slave letting the master know it properly received the data. The master then again pulls the line low to end the data transmission.
