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Old Jul 6th 2010, 10:51 PM   #1
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Logic gate circuit

I hope this is in the right section.
Design a circuit that will give the following truth table:
Inputs Output
A B
0 0 1
0 1 0
1 0 1
1 1 1


I can't make head or tail, the main issue is the second row of the table, I can't seem to get it right. I thought of using a main output a OR gate, then having one input from A always (1) but zero when the input at B is (1), but I cannot work that out. For these kinds of circuits, do I work from the output back, or the input forward? as in do I start with the output gate, then work to the input or vice versa?
Thanks
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Last edited by arze; Jul 7th 2010 at 12:21 AM.
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Old Jul 7th 2010, 12:19 AM   #2
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A is connected to one input of a nand gate. B is connected to the other input of the nand gate through a not gate. Out put is taken from the nand gate.
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Old Jul 7th 2010, 12:31 AM   #3
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do you mean it like the attached figure?
Or is it the A connected to a NOT gate to one input of the NAND gate with B connected straight to the other input?
Attached Thumbnails
Logic gate circuit-circuit.jpg  
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Old Jul 7th 2010, 12:42 AM   #4
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Originally Posted by arze View Post
do you mean it like the attached figure?
Or is it the A connected to a NOT gate to one input of the NAND gate with B connected straight to the other input?
Replace NAND gate with OR gate. Check the truth table.

Last edited by sa-ri-ga-ma; Jul 7th 2010 at 12:54 AM.
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Old Jul 7th 2010, 12:45 AM   #5
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I checked the truth table, it works the other way around. i.e. A through the NOT gate to the NAND gate
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Old Jul 7th 2010, 01:18 AM   #6
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Use an OR gate. Let A be one input and B followed by a NOT gate be the other.
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Old Jul 7th 2010, 01:40 AM   #7
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that way works also!
Thanks!
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Old Sep 6th 2010, 10:23 PM   #8
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Circuit

Use AND for 1,2 and 4 positions and NOT+AND gate in the third situation.

The circuit will be

1*1=1
0*1=0
1*0=0 but with NOT gate the result will be
1*1=1 (using NOT at B input of AND)
1*1=1

Last edited by arbolis; Sep 7th 2010 at 07:55 AM.
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