Author Topic: Logic Gates  (Read 3330 times)

Offline frenulem - No.5417

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Logic Gates
« on: November 26, 2010, 11:39:55 AM »
Logic circuit – The chip that the gate is housed in.
Logic gate – The actual process that goes on inside the chip.

There are two chips that logic gates can be housed in,

CMOS integrated circuit
•   Supply rails between 0 to +5-15v
•   I/O threshold needs to be halfway between the supply rails. So if the supply rails are 0 and 9v then the logic gate will read the input as off when it receives a voltage of 4.5v
•   Is very prone to static damage

TTL integrated circuits
•   Supply rails MUST be 0-5v
•   Anything below 1v is considered 0 or Off
•   Much more robust than the CMOS IC less prone to static damage

The two main things you need to know about logic gates are that they can only work off of digital signals, analogue signals are too unstable to be used, and they can only have two states,
On  = 1
Off  = 0
 

There are 7 logic gates,
     1.   AND
     2.   OR
     3.   NOT
     4.   NAND
     5.   NOR
     6.   XOR or EXCLUSIVE OR
     7.   XNOR
Truth Tables
To find an input and output of a logic gate you need a Truth Table, these will display the inputs and outputs, genrelly they have 2 inputs and 1 output. i label my Inputs A and B, my output Q
           
            Inputs >  A  B | Q  < Output
Input A is high >   1  0 | 1   < This means the Output is high
                            ^
                        Input B is low

A cookie for whoever can tell me what gates this can represent
[spoiler]OR / XOR / NAND[/spoiler]
AND

 
The AND truth table
A   B | Q
0   0 | 0
0   1 | 0
1   0 | 0
1   1 | 1

This gate will only become high (1) when both Inputs are high (1)

The AND gate can be used in such places as an outside light with an IR sensor, One input will be to detect if its dark, the other to detect if there is a person coming up the path.
Also the AND gate can be made with normal components as such ...


OR


The OR truth table
A   B | Q
0   0 | 0
0   1 | 1
1   0 | 1
1   1 | 1

The OR gate will become high (1) when one or both of the inputs are high (1)

The OR gate can also be made without the chip with the components as such ...


NOT


The NOT truth table
A | Q
0 | 1
1 | 0

The NOT gate inverts (changes) the input signal, so if the input is high (1) the output will be low (0)

NAND


 The NAND truth table
A   B | Q
0   0 | 1
0   1 | 1
1   0 | 1
1   1 | 0

The NAND gate will not give a high (1) output when both inputs are high (1)

The NAND gate is called the universal building block as you can make all other gates using the  NAND gate wired up in different ways more on that later though. later is now ;) NAND Logic

NOR


The NOR truth table
A   B | Q
0   0 | 1
0   1 | 0
1   0 | 0
1   1 | 0

The NOR is the complete opposite of the OR gate, this only allows a High (1) output when both inputs are low (0)
XOR


The XOR truth table
A   B | Q
0   0 | 0
0   1 | 1
1   0 | 1
1   1 | 0

The XOR is a true OR gate beacuse it only allows one Input to be high (1) to give a high (1) output.

XNOR


The XNOR truth table
A   B | Q
0   0 | 1
0   1 | 0
1   0 | 0
1   1 | 1

The XNOR gate is the same as the NOR gate but allows both inputs to be high (1) to give a high (1) output as well as both inputs being low (0)
« Last Edit: December 08, 2010, 06:06:48 AM by frenulem »

Offline frenulem - No.5417

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Re: Logic Gates
« Reply #1 on: November 27, 2010, 04:11:31 AM »
That's all i need :) vids coming asap and any suggestions from anyone would be welcome. Potential dividers after this?
« Last Edit: November 27, 2010, 04:18:48 AM by frenulem »

Offline HiddenVenom

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Re: Logic Gates
« Reply #2 on: November 27, 2010, 01:09:20 PM »
What about XNOR?

Offline frenulem - No.5417

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Re: Logic Gates
« Reply #3 on: November 27, 2010, 01:22:37 PM »
Cheers, Going up now

Offline FOOKz™

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Re: Logic Gates
« Reply #4 on: November 28, 2010, 12:24:07 AM »
NAND
AND
NOR
OR
INV
XOR
XNOR

BTW close the topic so nobody can post to it(keeps the post clean). Good work dude keep it up. Every night i've been adding material to the ones i have already.

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Offline frenulem - No.5417

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Re: Logic Gates
« Reply #5 on: November 28, 2010, 12:30:13 AM »
I don't think i have the power to do that :/

Offline FOOKz™

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Re: Logic Gates
« Reply #6 on: November 28, 2010, 12:35:53 AM »
do you have xbox live?


Also keep it nice and colorful ;)

heres a template i has started: https://www.acidmods.com/forum/index.php/topic,35955.msg271471.html#msg271471

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Offline frenulem - No.5417

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Re: Logic Gates
« Reply #7 on: November 28, 2010, 01:18:24 AM »
I will ;)

yeah, gamertag is = frenulem not on atm, need to renew my subscription be back end of sunday/monday GMT

 

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