The I²C protocol has a two wire interface, meaning that the bus only has two signal lines of clock and data in which every device on the bus connects to. When a master wants to communicate with one of the devices on the bus, it sends a start bit followed by a control byte. The illustration on the lower right shows a typical EEPROM control byte. The first four bits of the 8-bit control byte are called the control code and are defined by the product data sheet. The master sends the assigned control code to address a certain device on its bus. Generally, serial EEPROMs are assigned a control code of 1010, as shown on the slide. The address pins are used when the master needs to call out a specific EEPROM on the bus.