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[on:]

I may be the only one to have encountered this limit, but the Windows IDE doesn't support comports beyond COM256.

COM256: All is well.
COM257: Appears in Device Manager and many other apps, however the "Serial Port" menu is greyed out in the IDE. If I edit preferences.txt to reference COM257, I receive the error "Serial port 'COM257' not found..."

Platform: Windows 2000 & Arduino 11

[Reply #1 on:]

Hmm, my guess would be that RXTX (the library we use for serial communication) only checks the first 256 numbers to see if they're real com ports.  (I'm pretty sure it finds them by simply guessing possible names and checking if they exist, rather than actually getting a list from the OS.)  I'm not sure this is common enough to worry about, though.

How'd you end up using COM257?

[Reply #2 on:]

I'm not sure this is common enough to worry about, though.

I'd say this is odd enough it likely doesn't matter yes.

How'd you end up using COM257?

I have two machines dedicated to programming FT232s, both are currently up around COM500. When the Arduino IDE didn't recognize the serial port, I started deleting device IDs until I could test for 254,255,256, and 257.