The NOT gate
The NOT gate (or inverter) has a single input and does the opposite: 0 becomes 1, 1 becomes 0. It is the only gate in the game with one input, and it is combined with all the others.
In real life
A “normally closed” switch: current flows as long as you do not press it. The “door open” warning light in a car, which comes on when the sensor says NOT closed. In programming, NOT reverses a condition: “if the file does NOT exist, create it”.
The truth table
| A | S |
|---|---|
| 0 | 1 |
| 1 | 0 |
The symbol
The classic symbol is a triangle followed by a small circle (the “bubble” that means inversion). The European symbol is a rectangle with a 1 inside and a small circle on the output. The 74HC04 integrated circuit contains six inverters.
Your turn to play
Place the right gate and flip the inputs: when every row of the table is green, the lamp lights up.
Your turn: 4 questions
Answer and see straight away whether you were right. You need 3 right answers out of 4 to pass the page. Your score stays on this device, nothing is sent.
Frequently asked questions
What does a NOT gate do?
It inverts its input. If the input is 1, the output is 0, and the other way round. It is also called an inverter.
What is the bubble on a gate symbol for?
The small circle shows an inversion. An AND gate followed by a bubble is a NOT-AND gate (NAND).
Can you put two NOT gates in a row?
Yes: two inversions cancel out, so the output equals the input. In practice this is sometimes done to buffer (strengthen) a signal.
The other gates: The AND gate · The OR gate · The XOR gate · The NAND and NOR gates · The truth table · All the pages