C-MOS R-S Flip-Flop


It's possible to build an R-S flip-flop using NAND gates. This project proves it! (If your memory needs refreshing about how an R-S flip-flop works, take a look back at project TTL R-S Flip-Flop 1).

After you finish the wiring connections, turn power ON. You will see either LED 1 or LED 2 light up. Press S1 and S2. What happens to LED 1 and LED 2?

Can you guess which represents the set state and which represents the reset state?

When LED 2 lights up, the R-S flip-flop is in the set state. When LED 1 lights up, the R-S flip-flop is reset. When you get the flip-flop set or reset, try pressing the key and see what happens. You see one of the prime characteristics of the R-S flip-flop - once the circuit is set or reset, the circuit keeps that state until an input signal causes it to change.

This means the R-S flip-flop can "remember" things. More advanced circuits like this one are used in computers so they can "remember" things as well. We'll tell you one thing.

Try to press S1 and S2 at the same time. What happened to LEDs?

This is a weak point of the R-S flip-flop in a sense. So you should pay attention to this operation when you design a circuit using R-S flip-flops.








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