Extreme NXT: Extending the LEGO MINDSTORMS NXT to the Next Level, Second Edition

Chapter 13. I²C Bus Communication

The I²C communication bus capability of the NXT is a powerful feature that allows practically unlimited expansion of inputs and outputs. Originally developed by Philips Inc., I²C stands for Inter-Integrated Circuit. Although physically located on the NXT sensor input ports, it's actually used for expanding both inputs and outputs.

Only three wires are necessary for I²C because the data is transmitted serially, or one bit at a time. One wire is used for sending and receiving data (SDA), while the other provides a synchronizing clock signal (SCL). On the input port connector, SDA is pin 6, and SCL is pin 5, or blue and yellow in the NXT cable. You need a third wire for ground, which is either pin 2 or 3, black or ...