Addressing with Dip Switch or ???

[skimask]

And if there is a better way, what would the maximum addresses I could have be? I am using a 16F628 with three available I/O pins.

Short of reprogramming each unit? Probably not...

3 free I/O's...

8 combinations using logic level I/O (high, low)...

Could have 27 using logic level, plus an Open state (high, low, open)

Could have practically unlimited options using RCTIME and a big handful of 1% (or better) resistors along with a tight tolerance capacitor... Combine a few pins using RCTIME and those same parts, and you could, in theory, have 2^48 combinations (not gonna happens, but it's theorectically possible).