Hello Dave,

>The attached diagram shows another possible solution.
    <SNIP>

    your method is very interesting. Do you have it actually built and
tested?

    Just a question. Does the 44780 based LCDs have pull-ups on the inputs?
If not, I don't think this will work.

>5. Read Port D to obtain the key states.  Any keys pressed along the X1
>row line will be indicated by 0's in the Port D bit positions
>corresponding to their associated column lines Y1 through Y4; unpressed
>keys will be indicated by 1's in their respective bit positions.

    Let's say no keys are pressed. You've charged all the caps with current
passing through the diodes, then you havn't discharged any caps because no
key are pressed when you turned RD4 LOW. Then you have RD7:RD4 as inputs
reading LOW, because no current passes from the cap to the port by the keys.
No current also passes through the (now reversed) diodes.

    How can this work?

    Thanks,

    Brusque

-----------------------------------
Edson Brusque
Research and Development
C.I.Tronics Lighting Designers Ltda
Blumenau  -  SC  -  Brazil
www.citronics.com.br
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