FTDI and windows com port allocation

Hi, I have two AVR4809s and each one has an FTDI connected to facilitate serial coms through the PIO serial monitor for the one AVR and through the arduino serial monitor for the other AVR. It all works fine, but something odd is going on. So when I connect the FTDIs to a USB hub, they usually report in device manager as COM12 and COM17. When they report in this way, my serial comms over both of the ports work as expected - I can send and receive from both serial monitors.

However, on power up of the USB hub, one of the FTDIs sometimes reports as COM16. When it does this, if I select COM port 16 in the arduino IDE for the serial monitor, serial comms with that device works fine, but the device connected via COM17 doesn’t work, i.e. I can’t send receive over the PIO serial monitor.

I don’t think this is a PIO problem, I haven’t done it, but I’m guessing if I use PORT16 on PIO and 17 on arduino sermon, the problem will go with the device, I hope I explained that ok.

If anyone has any thoughts on this I’d appreciate it.

thanks for help.

The problem is worse / different from what I originally thought and I don’t think I’ve got it properly defined as yet. I’ve had to revisit my testing, which I thought was complete :frowning:

I’ll post back when I have further information. Just fyi, FTDI have a comport utility which allows assignment of COM ports to devices.
I’ll post back if I can define the problem.

After inserting some Led logic to test that code was running as expected, one problem turns out to be the wire used to connect to the FTDI Rx pin. It was broken within the insulation (that’s me with the wire strippers I guess :frowning: )
I placed a led in my Serial.available() code block to toggle on serial receipt. It didn’t toggle.
I’m not sure that will explain the port allocation variance in Windows. I’ll report back.