The BBC Microbit V2’s I2C interface usage is different to it’s predecessor. It has two I2C interfaces : an internal one to talk to the on-board accelerometer/magnetometer and an external one for user supplied sensors. Traffic on the internal I2C bus is only visible on tespoints (TP20 and TP21). This makes it difficult to debug/view the internal I2C bus traffic. I had no springloaded test pins to press on to the testpoints so a quick hack as shown above provides just enough pressure on the pads to make an electrical connection. The orange and purple wires are coiled like a spring which causes them to press into the board. These wires are then connected to a logic analyzer via the breadboard. The analyzer displays the following data:
The I2C clock frequency seems to be 400kHz. There appears to be some kind of clock stretching going on also. The trace shows a read from the on-board accelerometer.