Good idea - AND the outputs through a diode/resitor AND gate.  As the key-scan
routine only uses one line at a time, there should be no conflict.

David

wouter van ooijen & floortje hanneman wrote:

> I might be blind but I don't see the big problem. The high nibble drives the
> control lines, and (via D+R) the key rows. The low nibble drives the LCD
> data pins and reads the key columns (use pull up or down R's). The only
> snatch is that to scan one row you'll have to toggle E, which can cause an
> operation on the LCD. To get around this problem:
>
> - make sure the operation is a no-op, like reading, or writing to a location
> that does not matter (maybe one of the user-defined characters)
> - reverse the operation immediately afterwards (for instance erase the char
> just written)
> - you have a pin 'left over' (or two, when you don't read). Use them all to
> drive E in and-fashion (you can use a D-R and gate, I think that does not
> count as active?)
>
> It is a pity I have no time to try this (one-hand typing with a baby in the
> other arm is difficult enough).
>
> Wouter van Ooijen
>
> Van Ooijen Technische Informatica: http://www.voti.nl
> Jal compiler for PIC uC's:  http://www.voti.nl/jal
> PICs kopen? http://www.voti.nl/shop
>
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