22 Jan
2012
22 Jan
'12
11:08 a.m.
Chuck Guzis wrote:
But many PC keyboards implement [n key rollover] also.
I wouldn't say "many", as it was always a small fraction. The vast
majority did not have diodes or any other technique to prevent ghosting,
and only offered two key rollover, which is generally satisfactory for
most typists. It was common for some of the "special" keys (shift,
control, alt) to not be part of the scanned matrix, so you could detect
any number of those, but not reliably detect more than two "normal" keys
at once.
The USB HID spec stupidly limits USB keyboards to reporting a maximum of
six key depressions. I have not seen *any* USB keyboards with diodes or
other antighosting. Maybe some of the high-end "gaming keyboards" do.
Eric