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Topic: Coms port- recognises Arduino until I click upload (Read 406 times) previous topic - next topic


I am working with some arduino mkrfox1200 and so far have had no problems. I've been able to upload code, read off the serial monitor etc.
I have come back to work on them today, and to start of with I re-upload basic code that I know works such as blink.
The IDE recognises that my arduino is plugged in, and is set to the right board however as soon as I click upload it loses coms with the board and no longer shows it as an option on the port selection part of the menu.
It is doing this with all of the arduinos- they are brand new boards so shouldn't be a problem there.

When I close Arduino and restart it, it recognises the board again and then loses it as soon as i try to upload...

Any ideas?


no longer shows it as an option on the port selection part of the menu.
Does any port for the board appear under the Tools > Port menu? I've heard of the upload causing the port to change, but not of it causing no port at all to show until the IDE is restarted.

Which version of the Arduino IDE are you using?

Which OS are you using?

Which other Arduino boards have you encountered this issue with?


Hi @pert- thanks for your help!  :)

When it does show the one the arduino is connected to, it often changes number ie from "coms3 arduinomkr1200" to "coms6arduinomkr1200" without me changing the port plugged into. However, the issue is that now it isn't showing any coms with the arduino attached, and I can just see other coms such as "coms3" but none with a link to a board.

I am using windows with the IDE version 1.8.5.

All the boards I have used have been the ArduinoMKRfox1200, however I have multiple of these boards all experiencing the same problem.


I was actually able to reproduce this issue with my MKR Fox 1200, but I'm not at all sure we have the same issue, since mine would only occur under a very specific set of conditions.

I have been having a problem lately where Windows enumerates new virtual COM port devices to the same COM port as a device I already have on my system. This causes the new device to not appear under the Arduino IDE's Tools > Port menu. This only started in the last few weeks. I've never had this problem in the decades I've been using Windows. This was my first time using my MKR Fox 1200, so I plugged it in and then went through the hassle of changing the port number of the MKR Fox 1200 so that it had it's own unique COM port. After doing that, I tried an upload. The upload failed and then there was no port listed in the Tools > Port menu for the MKR Fox 1200! I noticed that the built-in LED on the board was pulsing steadily, indicating it was remaining in bootloader mode. When the bootloader on the MKR Fox 1200 runs, it enumerates to a different COM port than the board has when your sketch is running. The Arduino IDE is able to handle this during uploads by looking for the port that appears after the reset signal is sent, then uploading to that new port. But in my case, Windows enumerated the bootloader port to the same port as a different device, causing the upload to fail. Because the MKR Fox 1200 stayed in bootloader mode after that, it never switched back to the non-bootloader COM port, which I had already fixed. So I went through the same process of reassigning the bootloader COM port to a unique port number, and now my MKR Fox 1200 is working fine.

So, in order for this to be the same problem as your having it would require that:
  • Windows is enumerating the bootloader COM port to a non-unique port number. You can check this by opening the "Ports (COM and LPT)" section of Windows Device Manager and checking whether you see a port for "Arduino MKR Fox 1200 bootloader" which has the same number as another device on that list.
  • The MKR Fox 1200 is remaining in bootloader mode. This will be indicated by the on board LED pulsing. The COM port of the MKR Fox 1200 will also have the word "bootloader" in the name.

Even if that's not your exact problem, it still is helpful for you to look in Windows Device Manager after the problem occurs to see whether it's only the Arduino IDE that doesn't see the COM port, or if it's also missing in Device Manager as well.

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