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Questions tagged [logic-gates]

Symbolic representation of ideal devices implementing boolean functions

Logic gates are symbolic representation of ideal devices implementing boolean functions. See

Logic Gates Wikipedia Article

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Why are NAND gates used to make AND gates in computers?

Why is this a standard for AND gates when it could be made with two FETs and a resistor instead?
theonlygusti
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What is the purpose of a buffer gate?

As I understand a buffer gate is the opposite of a NOT gate and does not change the input: However I sometimes see buffer gate ICs used in circuits and to an inexperienced eye they seem to do nothing at all. For example recently I've seen a…
I have no idea what I'm doing
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What is the process of going from machine code to electrically controlling individual transistors?

For someone who writes software but doesn't have a computer engineering background, the dozens of abstraction layers have always bewildered me. I know all source code in their most fundamental level is broken down into 1s and 0s. I also know all…
master_of_privates
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Why does a single AND gate need 60 transistors?

Looking at the datasheet for the MC74VHC1G08, under the features section, it states Chip Complexity: FETs = 62. Why does this IC need 62 transistors, while an AND gate can be made with only 6 transistors? What are the other 56 transistors being…
eeze
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Why would an AND gate need six transistors?

I'm taking a digital design course, and I've been told that a NAND gate needs four transistors to implement and an AND gate needs six (four for a NAND gate and two for an inverter). That makes sense until one of my classmates told me he could…
Dev-XYS
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Three legged NOT gate? What is this symbol?

I've come across the above schematic in a datasheet for a 4x2:1 bus switch. What exactly does that triangular symbol on S mean? It looks a lot like a NOT gate, but the third leg is confusing me.
Bo Thompson
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What will happen if the output from a NOT-gate injected- BACK to its OWN input?

Not-gate, if get a 0(Off) input, it gives an 1 (On) output. And if get a 1 (On) input, gives-back a 0(Off) output. Now, if-I could bring the output back to the input of the not-gate, then what will happen? If the gate is getting a 1 input, it is…
Always Confused
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Why is the + sign commonly used as logic OR operator?

A few days ago I was asked, why it is pretty common to use the + instead of the v symbol as the boolean OR operator in digital logic. His argument was, that it is totally counter intuitive to use + for OR, because it is more likely to be interpreted…
Rev
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OR gate vs. connecting two wires?

I am not much of an electrical person but I'm trying to get an idea about it, so keep in mind I have very little background outside of college level electrical physics with calculus, and a strong basis in mathematical logic. I was learning about…
Alex Jones
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Why am I Seeing A Weird "Notch" on the Data Line For Some Logical 1s?

I'm attempting to build a Z80 homebrew computer for some retrocomputing fun and to teach myself the basis of electronic design. For proof-of-concept, I've already assembled a basic system on breadboards successfully in the previous weeks. The…
比尔盖子
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Diode Logic Gates

For some reason, I understand transistor logic gates, and I am able to solve problems, but for some reason I do not understand the and / or logic gates constructed by diodes. If someone can explain it to me using circuit analysis, I would appreciate…
user153322
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Why do two reverse diodes represent the logic gate AND?

Consider: I can make no sense in my head how this can work. How is it possible to have a current flow through normal diodes from cathode to anode and represent an AND if both are 1?
user165500
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What is the purpose of an AND gate with the same signal on both inputs?

If this is a buffer, why use an AND gate, aside from better availability of that gate in a single package? This is on an Analog Devices SHARC eval board.
jars
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Digital Logic circuit - exam question

I have a question from exam that I failed to solve: I need to build a digital logic circuit that is receiving 4 bit number and return true if the number is 0, 7 or 14. I have only one XOR gate (2 inputs), one NOR(3 inputs), one NAND(2 inputs) and…
nrofis
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What is the purpose of chaining series of NOT gates?

I have seen these a few times, but I don't know what the purpose is. Clearly the purpose is something else than just to invert the signal. Otherwise just one or two would be enough for that. Also, does this configuration have a name? simulate this…
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