source= http://www.piclist.com/postbot.asp?id=piclist\2003\04\11\174744a

Let me see if I have all this right. Combining Scott and Eric's comments you
could do this:

    0   1   2   3  GND
    |   |   |   |   |
0---+--KEY-KEY-KEY-KEY-
    |   |   |   |   |
1---+---+--KEY-KEY-KEY-
    |   |   |   |   |
2---+---+---+--KEY-KEY-
    |   |   |   |   |
3---+---+---+---+--KEY-
    |   |   |   |   |

Weak pull-ups enabled, first read the port and check for any lows, this
would be a key on the GND (far right) column. If all pins are high, ground
pin 0 and any lows on 1 thru 3 would be a key in the top row. Then ground 1
and a low on 2 or 3 indicates the two keys on the second row (other than the
last column), finally ground 2 and check the remaining key (on the third
row) by reading back 3.

That is a 10 key pad in 4 IO lines with no external components other than
the keys.

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