The C3 documentation specifies that you can't connect to USB (to computer) and external power at the same time.
"The Propeller C3 Is designed to accept power from the USB port or from an external power supply. Do not
simultaneously supply power from more than one source. Before supplying external power be sure to
remove the USB cable, otherwise damage to the C3 and your computer may occur."
(pp. 4, 18)
So, if we want to use external power and still communicate with a computer, we will need to connect a separate USB/logic-level adapter to the C3.
This would be something like a Prop Plug connected to the TX, RX, and GND of the System/Power Header if we want to use the same Prop pins (30, 31). Is it ok to do this? I.e., to have two FTDI chips both connecting to the same pins of the Prop (but only one connected to a PC)?
Otherwise, we will have to use up two more pins for USB i/o to avoid conflicts.
(I am anxiously awaiting the arrival of my first C3.)