The I²C bus is the most popular of the three current serial EEPROM protocols because of its simplicity, high signal density, and unique write protect (WP) pin characteristics. This illustration shows the typical pin-out of an I²C device with pins 1 through 3 as address pins A0, A1, and A2. Pin 4 is designated as ground, Vcc, while pin 5 is the data line, SDA. The clock signal SCL is at pin 6, pin 7 is WP, and pin 8 is voltage, VSS. An advantage of the I²C protocol is that it only requires two signal lines for clock and data as opposed to other protocols that require four signal lines between the EEPROM and the master device.