Date   : Mon, 19 Oct 2009 00:19:11 +0100
From   : afra@... (Phill Harvey-Smith)
Subject: New storage system suggestinons?

Ian Stocks wrote:
> I was thinking it should be possible to decode the inputs to the 7445 
> (IC26) for the current row being scanned, and then have an output port 
> connected to the inputs of the 8255 (IC25) to set the relevant pressed 
> key. One possible problem is the delay between decoding the row scan and 
> setting the output for a key being pressed.
> 
> Did you try doing it that way before using the crosspoint switch?

I thought about it, but had been down this road doing a similar thing 
with my Dragon 32 a couple of years back, and found it could be 
problematic. Especially with games which tend to bypass firmware and do 
their own keyboard scanning, which of course I have no way of second 
guessing.

At least with the crosspoint the Atom (or whatever) sees it as a matrix 
of switches, esactly like it's keyboard so it's garenteed to be compatible.

Also doing it this way simplifies things for the AVR too, as it just 
needs a translation table between the PC scan code and the row/column 
position on the keyboard, and all it needs to do is set/reset the switch 
at that position. So it does not need to have a copy of the keyboard 
matrix state as that is held in the crosspoint.

Cheers.

Phill.

-- 
Phill Harvey-Smith, Programmer, Hardware hacker, and general eccentric !

"You can twist perceptions, but reality won't budge" -- Rush.