Serial is supported on native-USB port as well as non usb ports (for example, /dev/ttyS6) for Pixhawk boards in the Embedded Coder Support package for PX4 Autopilots. A serial to USB FTDI converter is required for this.
The image below shows the connection of Serial 4 (/dev/ttyS6) on Pixhawk 1 board to the FTDI converter.
The table below lists Pin information for the Serial 4/5 port and its connection to FTDI for the Pixhawk 1 board. The pins described here are from left to right.
