What does the circles in the logic circuits mean?

[bitslice]

^ yep I can see that there will be different ways of approaching a problem and bubbles probably suits a larger scale design, and probably more like how chip designers think.
I've always looked if any complex TTL IC will do the job more efficiently, then looked at what logical operations to do on the incoming signals, then inverted the logic to suit an implementation.

Certainly from a testing viewpoint I reckon it's easier to not care what the design is supposed to do, but simply to see if what goes in relates to what is actually coming out.

[Galenbo]

I know those circles in the circuits mean 'Not' ... Every time I see a circle do I need to flip the values?How does it work?

Like said before, yes, and be aware of timing too.

You can see those circles in places where you think they are not necessary, and that can have multiple reasons.

For example: Sometimes a signal has to amplified/buffered/limited/filtered, and an easy way is/canbe to use an unused NAND port that is present anyway.

But now the signal is inverted? No worry, that's easily solved in software or port settings.