In article <pan.2003.12.16.14.28.08.932374 RemoveThis @spamhotmail.com>, "Valtteri"
<spamfiltsu RemoveThis @spamhotmail.com> wrote:
> hello!
>
> I have an old keyboard made apparently in 1989. I've kept it because it's
> unbeatable in splitscreen and other games where 2/3/4 players use the same
> keyboard. It can take almost any amount of simultaneus key presses without
> any trouble.
>
> The newer keyboards that I've come across don't seem to be
> able to do this and I was wondering whether any manufacturer was making
> keyboards that aren't limited by the number of simultaneus keypresses.
>
> Is it just that the technology currently used in keyboards doesn't allow
> that?
The feature you want is called "N-key rollover". It basically needs a
diode installed with each key switch, from what I remember, which raises
the cost of assembly. The following document shows how the diode is placed
to steer the current from the scan lines, so no phantom keys show up when
multiple keys are pressed.
<a style='text-decoration: underline;' href="http://www.cirrus.it/pdf/232_2863.PDF" target="_blank">http://www.cirrus.it/pdf/232_2863.PDF</a> (page 2)
I think the other kinds of keyboards were called "2-key lockout",
in that pressing a second key would be ignored. As far as I can remember,
the modifier keys on the keyboard were done separately, so they didn't
count.
One website I happened on, mentioned that you can blaim the loss of
this feature on membrane keyboards. If a keyboard has separate switches,
then the diodes can be used.
It's been a long time since I thought about this, because I built my own
keyboard when I was a kid. I used the diodes because I could. It was the
largest printed circuit board I ever made by hand, and it was very
difficult to get all the pins from the keys on the bottom of the key
assembly to plug into the bare PCB. Nice keyboard though.
Paul<!-- ~MESSAGE_AFTER~ -->
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