The number written near each pin on the silk screen indicates the GPIO number. The pin numbering starts from top left down to bottom right.
On each pin group are available the power supply lines (+5 volt, +3.3 volt and GND) and a set of GPIOs and control signals.
To keep the price as low as possible the CM3-Panel uses just the unique USB port available on the Raspberry compute module to communicate with external devices.
The following photo shows the differences between the two models.
Using an USB to serial interface it is possibile to access to the debug port serial lines available on EXP2 connector as shown on this photo:
The lines used are:
|33||Debug RX line|
|32||Debug TX line|
The serial setup is 11500,8,N,1