Logic gates question

Thread Starter

TaPaKaH

Joined Feb 4, 2008
2
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?
 

Dave

Joined Nov 17, 2003
6,970
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
 

Papabravo

Joined Feb 24, 2006
13,972
I do not think it is possible.
If you DeMorganize the gates you will see this clearly.
Low outputs require low inputs
 

Dave

Joined Nov 17, 2003
6,970
you have only high input and you must have a low output using ONLY AND and OR gates
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
 

Dave

Joined Nov 17, 2003
6,970
That is quite true, but completely irrelevant since an inverter is neither an AND gate, nor an OR gate.
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
 

mik3ca

Joined Feb 11, 2007
189
you have only high input and you must have a low output using ONLY AND and OR gates
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.
 
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.
 
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