TTL NOR gate
Try the same thing you've been doing with the past few Projects trace the "logic flow" of this circuit!
Start with a 0 or 1 input and see how this circuit arrives at a 0 or 1 output.
Give it a good try and don't peek at the answer. As you're building this circuit, set the Select Switch to B.
When you finish the wiring connections, turn ON the circuit. Press the Key. Is there any change in LED 1?
Release the Key and set the Select Switch to A. What happens to LED 1 now?
Leave the Select Switch at A and press the Key does anything different happen?
As you just saw, this Project behaves just like other NOR gates we've built. And it does so because ...
Don't believe us? Try putting a the schematic - see how it changes.