I am trying to use an FTDI breakout board to connect to my custom made Arduino compatible board. I am using a new 16 inch macbook pro with USB-c ports, so I am using a dongle, in case that could be the problem.

Every time I try and upload a sketch I get the error: "can't open device "/dev/cu.usbserial-D306P6WW": Resource busy". When I check the /dev/ folder, both "/dev/cu.usbserial-D306P6WW" and "/dev/tty.usbserial-D306P6WW" show up, however in Arduino IDE I can only choose the "/dev/cu.usbserial-D306P6WW" option. I have installed FTDI VCP drivers, CH340 drivers and all kinds of other drivers to try and fix this issue. I have restarted countless times, and I have used a multitude of commands to check for programs hogging the usb port, but there is never a program. Plugging a harddrive into the same port causes no problems, so the port can't really be the problem. I am using a "FTDI FT231XS" board from Sparkfun.

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    Do you have the Arduino serial monitor opened in parallel? Also, from where do you have the FTDI drivers? Have you unloaded the mac os kernel drivers before that? Feb 8, 2020 at 15:36
  • I don't have the serial monitor open. I downloaded the FTDI drivers from their website, and I have not unloaded any drivers? Do I need to do that? Feb 8, 2020 at 15:38
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    Hm actually I confused it with the CH340 installation process (github.com/adrianmihalko/ch340g-ch34g-ch34x-mac-os-x-driver). But that shouldn't be used for such a recent Mac OS version; also you don't need it because you don't have a CH340 chipset. If you followed learn.sparkfun.com/ftdiDriversMac you should be good. Can you open a root terminal and edit your question to include the output of kextstat | grep FTDI? Unplug and replug the FTDI board and post the recent dmesg output starting at the unplugging of the USB device. Feb 8, 2020 at 15:44
  • Thanks for your help, I tried a whole bunch of other things, and then decided I would update my Mac version. For some mystical reason this actually fixed the problem?! Thanks anyway! Feb 8, 2020 at 16:43

1 Answer 1


Nevermind, updating my MacOS version to 10.15.3 magically fixed the problem...

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