Physics Help Forum Logic gate circuit

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 Jul 6th 2010, 10:51 PM #1 Senior Member   Join Date: Feb 2009 Location: Singapore Posts: 206 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 __________________ To each his own. Last edited by arze; Jul 7th 2010 at 12:21 AM.
 Jul 7th 2010, 12:19 AM #2 Senior Member   Join Date: Dec 2008 Location: Udupi, Karnataka, India Posts: 292 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.
 Jul 7th 2010, 12:31 AM #3 Senior Member   Join Date: Feb 2009 Location: Singapore Posts: 206 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   __________________ To each his own.
Jul 7th 2010, 12:42 AM   #4
Senior Member

Join Date: Dec 2008
Location: Udupi, Karnataka, India
Posts: 292
 Originally Posted by arze 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.

 Jul 7th 2010, 12:45 AM #5 Senior Member   Join Date: Feb 2009 Location: Singapore Posts: 206 I checked the truth table, it works the other way around. i.e. A through the NOT gate to the NAND gate __________________ To each his own.
 Jul 7th 2010, 01:18 AM #6 Physics Team   Join Date: Feb 2009 Posts: 1,425 Use an OR gate. Let A be one input and B followed by a NOT gate be the other.
 Jul 7th 2010, 01:40 AM #7 Senior Member   Join Date: Feb 2009 Location: Singapore Posts: 206 that way works also! Thanks! __________________ To each his own.
 Sep 6th 2010, 10:23 PM #8 Junior Member   Join Date: Sep 2010 Posts: 5 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.

 Tags circuit, gate, logic