Use diode isolation at each output pin going to the keypad and
you will eliminate the problem.

Fr. Tom McGahee

----------
> From: Benjamin Petersen <benjamin@MARK-INFO.COM>
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: Remote keypads - which PIC?
> Date: Friday, May 14, 1999 4:12 AM
>
> > -----Original Message-----
> > From: pic microcontroller discussion list
> > [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Nuno Pedrosa
> > Sent: Thursday, May 13, 1999 7:44 PM
> > To: PICLIST@MITVMA.MIT.EDU
> > Subject: Re: Remote keypads - which PIC?
> >
> >
> > Can a keypad share pins with the bus to an LCD?
> >
> > What about keypresses? How do you keep them from interfering
> > with the LCD
> > comms?
>
> Be carefull !!!!!!!!!!!!! I have just designed at complete system with a
> '84, 8x4 keyboard and a 80x2 display.
> The display and keyboard share ports. Everything is okay except when i am
> writeing to the display and two or more keys (from different rows) are
> pressed at the same time. I do ofcause check if any key is pressed before i
> write to the display. But this is a lag of design (my fault). So please
> think again if it's worth it. They way i did was to share the 8
> row-keyboard-pins with the 8-display-data-pins.
>
> Regards
>   Benjamin Petersen