by Max » Sun Feb 22, 2015 2:48 am
They're both voltage OUTput, so you do not want to ever connect those 2 leads together. When using the serial header with a USB adapter, always remove the J4 jumper on AQ. Actually I don't even hook up the power wire from the adapter to AQ at all, just to be safe.
As to why the adapter is set up that way, I don't know. Maybe to remind you that the signaling voltage on AQ side is 3.3v.
-Max