# Logic gates question

Discussion in 'Math' started by TaPaKaH, Feb 4, 2008.

1. ### TaPaKaH Thread Starter New Member

Feb 4, 2008
2
0
hi, i need alittle help here.i have a question.
How can u have low exit when input is high, using AND and OR gates?

2. ### Dave Retired Moderator

Nov 17, 2003
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Just to clarify the question. Is this, how can you have a low output when one of the inputs is low, using AND and OR gates at the same time?

Dave

3. ### TaPaKaH Thread Starter New Member

Feb 4, 2008
2
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you have only high input and you must have a low output using ONLY AND and OR gates

4. ### Papabravo Expert

Feb 24, 2006
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I do not think it is possible.
If you DeMorganize the gates you will see this clearly.
Low outputs require low inputs

5. ### Dave Retired Moderator

Nov 17, 2003
6,960
144
No then. For an AND gate with one input tied to ground you will get a low output for a high (or low for that matter) input, but that is about it.

Dave

6. ### arthur92710 Active Member

Jun 25, 2007
307
1
An NOT or an inverter does what you need. High in Low out.

7. ### Papabravo Expert

Feb 24, 2006
10,148
1,791
That is quite true, but completely irrelevant since an inverter is neither an AND gate, nor an OR gate.

8. ### Dave Retired Moderator

Nov 17, 2003
6,960
144
My first instinct when I read the OP was, has the AND gate been confused with the NAND gate and the OR gate confused with the NOR gate - if so the answer is simple: to get a low output with a high input, just tie the inputs together - both the NAND and the NOR will then behave like an inverter.

Dave

9. ### Papabravo Expert

Feb 24, 2006
10,148
1,791
Well of course, but we should give the OP the benfit of the doubt, that he represented the question accurately.

Nov 17, 2003
6,960
144
Agreed.

Dave

11. ### mik3ca Active Member

Feb 11, 2007
189
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because logic gates require at least two inputs, and you only specified one input (which is high), and you didn't specify the other input. We will have to make your other input low.

you will have two outputs. One from the AND gate, and one from the OR gate.
you specified that you want One of these outputs to be low.

So walking through, we have:

Logic high, ORed with Logic low = High output on the OR gate.
Logic high ANDed with Logic low = Low output on the AND gate.

Now if you said your other input was high, then both outputs will be high.

12. ### James Sonroll New Member

Feb 22, 2008
4
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It is possible if you mean only one input is high and the output is low. Then, if you mean that all inputs and either one is high and the output is low, its impossible.

13. ### aliashar86 Active Member

Nov 23, 2006
71
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in the beginning dave gave a valid reason that ground the circuit nd u will get a low output

14. ### aliashar86 Active Member

Nov 23, 2006
71
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for further clarification u must see first the "Truth Table" of both AND nd OR gates