> Can you use a I/O port with internal pullups? Any way you slice it you will
> need 11 I/O lines (or more external hardware).

Not entirely true.  It would be possible to do this 8x3 with one pin (tough)
or 3 pins (easier), IF you pick the right pin(s); I guess this DOES fall under
"more external hardware", although that hardware is just resistors.

By using a pullup resistor on the columns and a pulldown on the rows (or
vice-versa), you can create a voltage divider which will produce a different
voltage depending on the button pressed.  Use a different resistance for
each row.  Now you can poll each of three ADC pins and, if the value is
in the right range, you know a valid button press has occured.

Not necessarily the best possible way, from a CPU overhead/software
simplicity point of view, but it's pretty easy on the pin count.

Mike H.
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