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AND? I Don't Understand: A Simple Explanation of AND logic function

Updated on January 25, 2015

Introduction

AND, in electronics or programming lingo, is a function that returns a 1 when all its inputs or conditions are 1. I know, you are probably saying “WHAT?? That made no sense!” Let’s start from the beginning. In electronics, logic gates are made from transistors and are the most basic part of an intelligent circuit. The function of a transistor is quite extensive; however, to make a logical circuit they are used to make 7 unique logic gates. These gates depend on the logical functions listed below:

  1. AND
  2. OR
  3. XOR
  4. NOT
  5. NAND
  6. NOR
  7. X-NOR

Understanding the lingo

Before we get into the details of the functions, let’s understand the lingo that I mentioned in the introduction. In electronics or programming, 1 means TRUE and 0 means FALSE. “I don’t get it”. Let’s try to understand using an example – When a light switch is switched to ON position, the light turns ON and when its switched to OFF position, the light turns OFF. “I knew that, how does that fit here?” ON means TRUE and OFF means FALSE. “So you are saying 1, TRUE and ON are all the same thing?” YES! And 0, FALSE and OFF are all the same. In fact, 1 can be said as TRUE, ON, HIGH or logical HIGH, it just means that a condition is TRUE. “What’s this condition now?” A condition is a situation, like in previous example, ON was the condition of the switch, which reflected the condition of the light. “Oh ok, so let me get this straight, when the switch is ON it means the condition of the switch is TRUE.” That’s exactly right!! And in return, the condition of the light changed to TRUE.

Learning by example

“OK I get that but how does this information explain the logical functions?” Let me tell you a small story. Steve and Marie have two children, Jack and Till. On a particular Sunday, Jack asked his father to take him to the zoo. Steve said, “We will only go to the zoo if Mum AND Jill want to go as well.” Jack said, “Mum wants to go but Jill doesn't.” “Maybe we can try to convince Jill as well” Steve said, “because, we will only go if Mum AND Jill agree.” In this little conversation, Steve kept saying “Mum AND Jill”, it means, that Mum AND Jill both have to say YES for them to go to the zoo. “Hang on hang on, so YES is the same as 1, TRUE and HIGH?” YES! The condition is that Mum AND Jill have to agree, so both conditions need to be TRUE in order for the family to go to the zoo. “I understand this, but give me another example.” OK, let me give you a scenario. Two light switches, switch1 and switch2, are wired in such a way that they both have to be ON in order for the Light to turn ON. What will be the condition of the Light if switch1 is ON and switch2 is OFF. “The Light will be OFF, obviously.” How did you figure that? “Well you said it yourself; switch1 and switch2 both have to be ON.” That’s it!

Technical stuff

“I think I am ready for the technical stuff. Hit me!” Alright then, the image below is of an AND gate and with it there is a table, that we call the Truth table in electronics lingo.

AND gate circuit symbol
AND gate circuit symbol
Input1
Logical function
Input2
Output
FALSE
AND
FALSE
FALSE
FALSE
AND
TRUE
FALSE
TRUE
AND
FALSE
FALSE
TRUE
AND
TRUE
TRUE
AND function Truth Table

Do you understand what this means? “I sort of understand it but why put options that won’t give a TRUE output?” That’s because for two inputs, we are putting all combinations or possibilities for input conditions. This means, that if we had three inputs, there would be eight combinations or possibilities for the input conditions. “Just out of curiosity, could I replace all FALSE in the truth table with 0, since they both mean the same thing, and TRUE with 1?” Bravo! That is exactly how the truth table is shown, let’s put it the right way. In fact, we don’t even need the Logical function column, since we already know what function we are talking about, however, for simplicity sake, I’ll leave it there.

Input1
Input2
Output
0
0
0
0
1
0
1
0
0
1
1
1
AND gate Truth Table

Ready for a challenge?

I believe you are ready for a challenge. “OK I’ll do my best.” This is a programming example but I have put it in words to keep things general to common programming languages. For RESULT of a student, GRADE is decided depending on the RESULT value. If RESULT >69 AND RESULT <80, the GRADE=Distinction. Keeping this condition in mind, if RESULT value was set to 65, would the GRADE value be Distinction? “Well, no because from your condition it seems you only want the GRADE to be Distinction if the RESULT value was between 69 and 80.” It’s actually 70 and 80, but besides that you are absolutely correct. You see “>” symbol means greater than, doesn't include 69. Technicality ;)

What's next?

This article is the first of a series of articles where we will explore other logical functions.

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    • profile image
      Author

      husnen 3 years ago

      Thanks for the comment Ron. This is my first article and its really nice to have an encouraging feedback.

      The idea behind my article is to show the readers that many concepts of computer programming or electronics, or physics as a matter of fact, may be understood using simple real life examples and events.

    • RonElFran profile image

      Ronald E Franklin 3 years ago from Mechanicsburg, PA

      Interesting way of explaining the AND function that should make it easy for non-technical people to "get" it.

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