Re: Multiple Keypress/release problems.

[Steve Baker <sjbaker1@airmail.net>]

Chris wrote:

> It is a hardware limitation, or rather a limitation built into the keyboard
> encoder ICs inside the keyboard itself and possibly the keyboard decoder
> circuitry on the motherboard.

Ack!  I thought that would be the answer - but had *hoped* that maybe there
would be a way out.

> I've no idea if USB keyboards are subject to
> the same restrictions.

Presumably - this is an attribute of the key decoding mechanism rather
than of the way the data is sent to the motherboard.
 
> http://www.ifbbc.com/html/did_you_know.html
> 
> may be of some interest. Most PC keyboards these days are membrane based so
> they will use the multikey option.

Well, it confirms the problem - but doesn't really explain what gets locked
out when what gets pressed.

So I'm left with...
 
> > * Does anyone know the rules that determine which keys will work with which
> >   key combinations?  Maybe I can work around it by picking just the right
> >   set of keys.
> 
> I believe it depends on the make of keyboard. For example I have two
> connected to my Linux box now - a no-name "multimedia" keyboard via PS/2 and
> my trusty Sun Type 5 connected to COM1. On the no-name the problem is exactly
> as you describe, but the type5 can handle wa and s but not 4 keys....

Hmmm - that's pretty depressing - but it does suggest that perhaps all *PC*
keyboards work the same way.  I could live with not supporting Sun keyboards
plugged into serial ports!

So I guess I need to find out how the row/column decoding is wired up to the
keys and *hope* that all PC keyboards do in fact work the same way.

Yuk!

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