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JongHwa
JongHwa

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[CS series] Understanding Logic Gates: The Language of Computers

Logic gates are the basic building blocks of any digital system. They take binary inputs (0 or 1) and provide a single output based on a specific rule.


1. AND Gate

The AND gate is like a strict boss. It only gives a "True" (1) output if all inputs are "True".

  • Rule: Output is 1 only if Input A and Input B are both 1.
  • Real-life example: You can enter the building only if you have a key card AND a password.

[Image of AND gate logic symbol and truth table]

2. OR Gate

The OR gate is more relaxed. It gives a "True" (1) output if at least one input is "True".

  • Rule: Output is 1 if Input A or Input B (or both) is 1.
  • Real-life example: You can get a discount if you are a student OR if you have a coupon.

3. NOT Gate

The NOT gate is also called an Inverter. It simply flips the input.

  • Rule: If the input is 1, the output is 0. If the input is 0, the output is 1.
  • Simple thought: It always says the opposite!

4. Universal Gates (NAND & NOR)

These gates are special because they are "inversions" of the basic gates.

NAND Gate (NOT + AND)

The NAND gate is the opposite of the AND gate.

  • Rule: It outputs 0 only when all inputs are 1. Otherwise, it outputs 1.
  • Fact: It is a "Universal Gate" because you can build any other gate using only NAND gates.

[Image of NAND gate logic symbol and truth table]

NOR Gate (NOT + OR)

The NOR gate is the opposite of the OR gate.

  • Rule: It outputs 1 only when all inputs are 0. If any input is 1, the output is 0.

📊 Summary Table

Gate Input A Input B Output
AND 1 1 1
OR 1 0 1
NAND 1 1 0
NOR 0 0 1

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