Nice one thanks.

I'm still a little confused as to how to deal with the situation where
the switches are NOT enabled (ie common portion floating) and you are
accessing the LCD when TWO or more switches are pressed. Surely this
will short two data lines together and invalidate the data to/from the
LCD ?

Please excuse my ignorance on this - it is my first (very ambitious) PIC
project.

       \\\|///
     \\  - -  // "Yes it IS safe
      (  @ @  )   to switch on"
+---oOOo-(_)-oOOo------------------+
| Mark Birks                       |
| Hardware Section Leader          |
| OmniBus Systems, Stanford House, |
| Stanford-on-Soar,                |
| Loughborough, Leicestershire. UK.|
|                                  |
| Tel/Fax: +44 (0)990 004300/333   |
| E-Mail: markb@omnibus.co.uk      |
|   ooo0                           |
|  (    )   0ooo                   |
+---\  (----(   )------------------+
     \_)     ) /
            (_/


> ----------
> From:         Jason Wolfson[SMTP:jason@MA.ULTRANET.COM]
> Reply To:     pic microcontroller discussion list
> Sent:         29 October 1997 18:42
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Re: A stupid question but...
>
> Mark,
> I did this with a 20x4 LCD and it worked great,
> check out my code at   http://www.ultranet.com/~jason
>
> I put the 4 buttons at each corner of the display and you
> put up a message to their function depending on what you want when...
> Kinda like an ATM machine....
>
> Jason
>
>
>
> -----Original Message-----
> From: Mark Birks <m.birks@OMNIBUS.CO.UK>
> To: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
> Date: Wednesday, October 29, 1997 12:04 PM
> Subject: A stupid question but...
>
>
> >Is it possible to multiplex the scanning of 4 push-button switches on
> >the same 4 'data' lines as an LCD module is using ?
> >
> >I've sort of thought along the lines of having all of the switches
> >commoned at one side and then having an OPen -collector arrangement
> to
> >short the switches to ground at read time.
> >
> >The drawback with this arrangement is that when the switches are NOT
> >being read and one or more switches are closed, data lines will be
> >shorted together. Adding diodes seemed like an obvious step forward
> but
> >the 0.7V drop takes them to the top end of the TTL logic '0' level.
> >
> >Anyone got any suggestions please ?
> >
> >Also I am looking at using a standard 16x2 LCD with these switches to
> >allow menu selection and configuration settings - has anyone done
> >anything that allows the PIC to communicate with a host processor (in
> >this case it is ACORN podule bus) to download menu choices,
> selections
> >etc. I am trying to reduce the amount of processing done by the host
> so
> >that the PIC can deal with most of the menu control if poss........
> >
> >       \\\|///
> >     \\  - -  // "Yes it IS safe
> >      (  @ @  )   to switch on"
> >+---oOOo-(_)-oOOo------------------+
> >| Mark Birks                       |
> >| Hardware Section Leader          |
> >| OmniBus Systems, Stanford House, |
> >| Stanford-on-Soar,                |
> >| Loughborough, Leicestershire. UK.|
> >|                                  |
> >| Tel/Fax: +44 (0)990 004300/333   |
> >| E-Mail: markb@omnibus.co.uk      |
> >|   ooo0                           |
> >|  (    )   0ooo                   |
> >+---\  (----(   )------------------+
> >     \_)     ) /
> >            (_/
> >
>