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Logic Circuit Help

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swiz747

New Member
Hi, I was wondering if there is an easier way of creating a 3 input 6 output logic circuit?

Truth Table
A B C ...U V W X Y Z
0 0 0 ...1 0 0 0 0 0
0 0 1 ...0 1 0 0 0 0
0 1 0 ...0 0 1 0 0 0
0 1 1 ...0 0 0 1 0 0
1 0 0 ...0 0 0 0 1 0
1 0 1 ...0 0 0 0 0 1
1 1 0 ...0 0 0 0 0 0
1 1 1 ...0 0 0 0 0 0


I would really rather not build this using AND/NOT/OR gates but if it comes down to it ill just bite the bullet. Also Ive used Multiplexers before but since the ones i used only had one output it wouldn't cut down too much on the amount of ICs i would have. Oh I almost forgot the ICs have to be cmos.
 
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MikeMl

Well-Known Member
Most Helpful Member
How about a CMOS 4028, where you strap a zero to D, and use only the 3 LSB inputs A,B and C, and take your outputs from Q0 to Q5?
 

Grossel

Well-Known Member
An demux, 74138 combined with a NAND gate should work. The NAND gates inputs should connects to your A and B counter output. The output of the NAND should be conected to the G2 (enable) input of the demux.

Only one little problem is left over now. All outputs from the demux goes HIGH instead of LOW, as you wanted. A workaround would be using a total of 8 NOT gates, one for each demux output. Also, you'll need to set demux input pin G1 to HIGH.
 

MrAl

Well-Known Member
Most Helpful Member
Hi,


There's also the 74xx538 which has true outputs unlike the 74xx138 which has inverted outputs. Not sure how hard one might be to find however.
 
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