Re: cross point switch

From: Jim Brain (
Date: 2004-05-20 08:26:29 wrote:

>Hi Jim,
>The idea I've had is to use an EPROM. 8 address lines in, 8 datalines out.
>One CIA drives the addresses (that is the one which outputs the scan value)
>the other accepts the output from the EPROM. You might need diodes on the
>datalines to create wired-AND with the joystick port. I expect this would be
>compatible with most things, except for any software which tries to swap
>which of the CIA outputs and which is the input...
I'm intrigued, because I do not understand.  I've seen EPROMs been used 
as address decoders, but in this case, the decode needs to change...

You could create all possible combinations or 1 and 2 key presses as 8 
byte maps, and use the controller for the high bits (select which map is 
decoded by manipulating AD9-15 of a 64 kB map.  However, that's a lot of 
maps (I calc 1024 maps or so, which works in a 8KB EPROM, I suppose.

Hwoever, I think there's some SW that scans the keyboard another way, so 
a one way solution would be unusable on those titles...

I'm interested in more information on your idea, though, as I must be 
misunderstanding it.


>-----Original Message-----
>[]On Behalf Of Jim Brain
>Sent: Thursday, 20 May 2004 10:28 AM
>To: CBM Hackers
>Subject: cross point switch
>I am trying to build a keyboard eliminator that does not require a cross 
>point switch to "emulate" the 64/128 keyboard.  However, in the event my 
>idea does not pan out, anyone know a part number for a 8x8 or so switch 
>that is not as big as the 40 pin monster on 64-KEYB?
>I'd like a plan B so my idea doesn't evaporate....

Jim Brain, Brain Innovations                      
Dabbling in WWW, Embedded Systems, Old CBM computers, and Good Times!

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