[geeks] new keyboard goodness

[Shannon]

On 19-Apr-2011 10:28, der Mouse wrote:
>>> Is Nkey rollover important though?
> 
>> Yes, very.
> 
>> I can type fast enough to outrun any keyboard without it.
> 
> ...huh?
> 
> What is rollover, then?  What I thought it was was the ability to
> correctly detect a key going up or down even with one other arbitrary
> key down (two-key rollover) or two others (three-key rollover) or etc,
> up to an arbitrary number of other keys down (N-key rollover).
> 
> Speed - of anything - is completely irrelevant to this property.

Speed is not irrelevant for two reasons: polling cycles and "touch
typing" wherein a second or more keys are struck before the first are
released.

Hitting more than one key in a polling cycle or striking further keys
before releasing currently down keys both result in matrix failures if
the keyboard does not have rollover. How much a keyboard is affected by
the polling cycle depends a lot on the controller. Also some broken
controllers have been released, like the Costar controller used in Das
Keyboard S and some of the Ducky boards.

Another method which isn't as good is to arrange the matrix so that
common multi-strike keys are all on the same X or Y line. This usually
allows 3-5 of those keys to be struck without error, but other keys are
still limited.

Without rollover (or the matrix hack) there are two things which will
happen. One is jamming, where the keyboard has been configured to drop
the third strike to avoid the fourth becoming a phantom from the matrix
short. The other is ghosting where you get phantom key strikes when
certain 3 key combinations are currently down.

Both can happen when typing fast or playing games.

BTW: Music keyboards are affected the same way.

The main issue is saving money on diodes needed to allow independent key
scanning.

The other issue is with USB which is not real good at detecting
keystrokes and is generally limited to 6 key rollover, also called 6KRO.