> Here's a simple test for your laptop keyboard: try LeftShift+RightShift+Q and see if it prints anything. Repeat with the other letters of the alphabet. In my

> Here's a simple test for your laptop keyboard: try LeftShift+RightShift+Q and see if it prints anything. Repeat with the other letters of the alphabet. In my case I get nothing for several letters such as X, T and M. Microsoft has published a table of key combinations that are required to work in Windows, and it does not include combos of two modifiers of the same type .. with one exception: Both Windows keys have to work together. (You'd not often find a laptop keyboard that has two Windows keys though) There's otherwise a convention when constructing (diode-less) keyboards to put the modifier keys outside the keyboard matrix altogether so as to guarantee that you'd avoid key-combo collisions with them. I.e. each of the Control, Shift, Alt/Option, Windows/Command/Super keys would get its own dedicated GPIO pin on the controller. BTW. On the old Amiga platform, the rollover issue was handled in a prudent way: Keyboards that did not have NKRO all had a standard keyboard matrix that was published in a reference manual which software developers could consult to figure out which key combos that were viable and which were not. Also here the modifier keys were outside the matrix.