# Student ? ( Logic Gates)

Discussion in 'Homework Help' started by radiobarn, Oct 29, 2015.

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There is a question, probably elementary but im new at this, ? Is Design, draw, and wire a 5 input NAND circuit using one 2 input OR gate, one 2 input NAND gate , and one 4 input NAND gate.

Ive been drawing this circuit for a couple hours and have no idea, I know a 5 input NAND gate will only go low if all inputs are high, but with the 2 input NAND in there going low with its inputs high, I cant solve how to build this circuit, please help. Thank you.

2. ### MikeMlWell-Known MemberMost Helpful Member

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Do you know how to apply DeMorgan's Theorem?

What happens if you tie the two input pins of the Nand gate together?

3. ### Les JonesWell-Known Member

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As this looks like a homework question just giving you the answer will not teach you to understand. So here is a tip. Apply DeMorgan's Theorem to the 2 input OR gate. The result will be a 2 input AND gate for NEGATIVE logic. The solution I came up with results in a 6 input NAND gate but you could just tie 2 inputs together or tie one input high.

Les.

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5. ### ronsimpsonWell-Known MemberMost Helpful Member

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1)At first I tried to take the OR + NAND and make some thing to go ahead the 4-NAND. In 20 seconds I could not see it.
2)What do we have? 4 input NAND + 2 input NAND
>>To make a 6 input NAND we would need (the 4 input NAND) OR (the 2 input NAND).

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Thanks for the replys, yes this is a lab question where we are supposed to draw a schematic and the build it out and test on a breadboard. I still cant seem to make anything that will act like a 5 input NAND from these components, Im not sure how the OR gate should have any relevance in the circuit, tying the legs together makes it irrelevant, tying the 2 legs of the 2 input NAND together makes an inverter, the closest thing I can come up is different combinations where all 5 inputs are high will result in a low output, but there will be other situations as well that give a low output.

7. ### MikeMlWell-Known MemberMost Helpful Member

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A = B+C = (or gate)
by Demorgan, A' = (A+B)' = A'B' implies output is 0 when both A is 0 AND B is 0. (Duality)

Does this give you any ideas how you could combine the outputs of the two NAND gates????

8. ### MikeMlWell-Known MemberMost Helpful Member

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Make a truth table for this circuit: It has four inputs, so only 16 states. What logic function is it equivalent to?

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