@ragb @TheQuinbox My mistake! I probably looked in the wrong directories. I had only come across GPL-licensed code, so I avoided reading it. I did find the protocol documentation in BRLTTY, though.I figured out the key press protocol by analyzing the bytes sent to the serial port. The prpblem was sending characters to the Braille display. It seems the data needs to be preceded by "escape+ B".I eventually figured out what was happening on Windows. It doesn't seem to be a screen reader issue, but rather that Windows immediately detaches the device from COM3 for some reason. I don't know why, as I haven't used Windows in about 25 years! It would be interesting to investigate this further at some point, though.By the way, are you the author of the BRLTTY and NVDA drivers for the Apex?