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Using MAX II CPLDs as Analog Keyboard Encoders
Application Note 426
July 2006, Version 1.0
Introduction
Keyboard encoders are a very common application for CPLDs. Typically a processor, ASSP, or ASIC does not have enough pins for keypads or keyboards. I/O expansion is a very common function for CPLDs and allows a processor to decode a very large keyboard with very few I/Os. Even though CPLDs like MAX® and MAX® II may have abundant low-cost I/Os, decoding a keypad or keyboard with one I/O per switch is not desirable. The advantage of decoding a keyboard with fewer wires is that it reduces the number of wires going from a keypad to a main circuit board or it reduces the complexity of a switch matrix in the keyboard assembly.
AN-426 Datasheet
