Ernie Murphy wrote:
>
> Ben,
>
> If I understood what you are doing right (and I just gave it a quick
> read... sorry) you can isolate the switches from your address lines by
> simply adding a series diode to each switch. You can press 2 buttons and
> all it does is connect the address lines with two back to back diodes...
> which doesn't conduct.
>
> Assuming you drive an address line high to see if a switch is closed, point
> the diode from the PIC output to each switch. If you output lows to detect
> switch closures, spin the diodes round the other way.

Have a look at:
http://www.dontronics.com/dt102.html
nice little schematic of it there.

Don McKenzie  mailto:don@dontronics.com http://www.dontronics.com

Don's Download Dungeon:   http://www.dontronics.com/download.html
Australian Electronics Ring http://www.dontronics.com/aering.html
Win $500USD Cash. Micro design contest:  http://www.simmstick.com