Given the way we connect our switch matrix, I guess our statement about phantom keys and rollover is, unfortunately, complicated.
Our keyboards will support any one to four modifier key combination ( Shift, Control, Alt or GUI keys) plus a fifth key as long as 1) no Left+Right modifier keys(Left+Right Shift, Left+Right Control, etc. ) are involved in the combination and 2) neither the Pause key nor the Caps Lock key are the fifth key. Our original intent was to support multikey sequences required by any Microsoft OS or Application and to the best of my knowledge, that's still true.
Of course our keyboards will support other key combinations larger than five key sequences without generating a phantom key situation and there are some 3 key sequences which will generate a phantom so it's difficult to a generic statement beyond the one above.
As for rollover, the HID and boot protocol standards limit our USB keyboards to six key rollover. The buffer sizes and key processing in our PS/2 controller limit those keyboards to 7 or 8 key rollover.
Thanks
- Zach