TTL XOR gate
Électronique / Electronic
7400

Back in Project DTL Exclusive OR gate you saw how an exclusive OR (XOR) gate works.

Since we've made up other digital circuits by combining NAND gates, you might suspect we could make XOR gates as well. We can, as this Project will show.

As you build this circuit, set the Select Switch to B. After you finish the wiring connections, turn power ON.

Press the Key does anything happen to LED 1?

Now release the Key and set the Select Switch to A. What does LED 1 do now?

Leave the Select Switch at A and press the Key. What happens to LED 1 ?

You can see this circuit behaves like the XOR gate you built back in Project DTL Exclusive OR gate.

The output is 1 as long as the inputs are different. But if both inputs are the same — either 0 or 1 — the output of the XOR gate is 0.

Put on your thinking cap and try to follow each 0 or 1 input through the circuit until you reach the output. It will help if you mark "0" or "1" on the schematic at tht input and output of each NAND gate.