22 Jan
2012
22 Jan
'12
1:53 p.m.
Chuck Guzis wrote:
Six-key rollover seems to be a good compromise;
While the USB HID spec allows for six keys, I've never seen a USB
keyboard that reliably did more than general (not "special" key) two key
rollover.
There are lots of anecdotes about recent PC keyboards (USB and non-USB)
supporting better than two key rollover, but most of those, on
investigation, don't hold up. Often it's just a report that some
specific three or four key combinations work OK, which proves nothing
about the general case. It's not N key rollover unless it works for
*any* N keys.
There are definitely some high-end, very expensive PS/2 interface
keyboards that have N key rollover, but not any for USB due to the
stupidity of the USB HID spec.