Sorry for the delay. Was out of town.
My original posting may have sounded a little strange as I was referring to both COM3 and COM4 as if this was in reference to the hardware but is actually a mix. Let me try again.
I am running this with 4.3 now. The custom board is wired for what would physically be COM4 (pins 200 and 167) but in the code I have had to use “COM3” as the string passed to the serial port when I create it so I can communicate with the device. If I use the string “COM4” in the code, there is no communications.
I already changed all the pin numbers and COM PORT names to suit the G400D. It was only COM4 that didn’t work until I change the code to use COM3.