>Each will require a different amount of I/O
>
>1) The 4 individual keypads would require 32 I/O lines
>2) The 8x8 would require 16 I/O lines.
>3) The 4x16 would require 20 I/O lines.
>
>In each case a decoder and/or multiplexer can be used to reduce the lines
to
>the corresponding power of 2. So for the cost of a chip, you can greatly
>reduce the number of lines required.

Why don't you use 4 A/D channels where each A/D channel reads a whole 4x4
keypad?  I've completed a project with a PIC18F452 where I read 8 switches
with one A/D pin.  It's not hard. If interested, I send you a schematic...

Carey Fisher, K8VZ
website: www.ncsradio.com

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