Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!samsung!uakari.primate.wisc.edu!dali.cs.montana.edu!ogicse!zephyr.ens.tek.com!tekcrl!tekgvs!toma
From: toma@tekgvs.LABS.TEK.COM (Tom Almy)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: Northgate keyboards do not have N-key rollover
Message-ID: <8182@tekgvs.LABS.TEK.COM>
Date: 27 Sep 90 14:39:05 GMT
References: <39363@shemp.CS.UCLA.EDU>
Reply-To: toma@tekgvs.LABS.TEK.COM (Tom Almy)
Organization: Tektronix, Inc., Beaverton,  OR.
Lines: 23


This posting has me baffled. *My* Northgate OmniKey/102 had N-key rollover.
What it is missing is anti-aliasing. With mechanical contact keyboards, this
is accomplished by adding a diode in series with each key. Many but not all
keyboards handle this*. You only get the phantom keys if you press three keys
at once, and then only certain combinations of three keys will do this.
If the keyboard is a straight matrix encoding of the physical key positions
(and the Omnikey seems to be this case) then you get the phantom key when
you depress three keys such that the third key is in the same row as one
of the keys and in the same column as the other. This will never happen
with standard typing since each finger is assigned its own column(s).

You can check to see if your keyboard has N-key rollover by pressing (but
not releasing) a-s-d-f in order. The four keystrokes should be accepted,
then the keyboard will start repeating the f. Without the rollover you
would only get the a or a-s (with 2 key rollover).

Tom Almy
toma@tekgvs.labs.tek.com
Standard Disclaimers Apply

* I just checked a nearby Mac II, and it generates the phantom keystrokes
as well.