> how can I only uses 5 cpu I/O pin for 16 keyborad keys input?
> THANK!!!!!!!

You might have a look at our EDE1144 4x4 matrix keypad encoder IC.  It will
allow you to read all sixteen keys using a single I/O pin, and adds features
such as key debouncing, keybeep, and automatic repeat when a key is held.  A
datasheet is available at http://www.elabinc.com/chips.htm

One tremendous advantage to using the EDE1144 over other keypad IC's is that
the keys are NOT continuously scanned (continuos scanning can cause
unintended radiation from the wires leading to the keypad).  Instead, stable
voltages are held on the keys and a query cycle scans once per keypress.

Todd Peterson
E-Lab Digital Engineering, Inc.

   (816) 257-9954  FAX: (816) 257-9945
   http://www.elabinc.com