Mechanical keypads are commonly available in two forms – matrix and common bus (depending on how individual switches are inter connected) :
There are multiple ways in which you can use a PSoC 1 to read mechanical keypads.
Appnote AN2034 shows you how to read matrix and common bus keypads, in both polled and interrupt modes.
The document and example projects can be downloaded from this page: http://www.cypress.com/?rID=2824
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