Remember, if you write a zero to a row, it will appear in a column only if a switch is closed. If it appears in more than one row, then you've probably struck more than one key. I recommend you guard against that, as it will produce confusing "sneak paths" which give false readings.

This has been discussed below, I jusr remember another issue:

If you do what comes naturally and configure the select lines as push-pull (they ARE outputs) you may hear a small poof if multiple keys are pressed.

So, DO rememeber, if you use a processor with configurable ports) that the outputs MUST be of the "weak pullup" type.

Did I do this? yes, but caught it before power was applied.

Erik