The expansion board provides a single “serial over USB” debug port that is intended to capture boot time flow and provide a command console to the module.
Although an inspection of the schematic shows component locations to support a high-speed UART debug port, high-speed UART functionality is not enabled.
Serial Debug Port (J9)
The debug port is mapped from the module to the expansion board as a standard Type-B interface; data lines are routed through an active ESD filter (U24) in route to a USB to UART translation device (EU6).
Expansion board reference designator EU6 is a FTDI* FT232RQ USB UART device. This device translates the 5 VDC USB communications into a 3.3 VDC UART protocol and also enables self-powered (from the expansion board +V5P0V boost regulator) or bus-powered operation when powered from the micro-USB Type-C connector.
After the USB debug information is translated to the 3.3 VDC UART protocol, it is further shifted from 3.3 VDC to 1.8 VDC by the EU14 before reaching the module.
See Workstation Setup for details about configuring a workstation to communicate with the development kit over the serial debug port (SDP).
Guidance for troubleshooting can be found in the Troubleshooting and FAQ on this site. Additional help can be found in the Troubleshooting and FAQ – Using the Intel® Joule™ development platform.