# Build Circuit with four inputs and two outputs

Discussion in 'Homework Help' started by vlucaj, Sep 21, 2015.

1. ### vlucaj Thread Starter New Member

Sep 21, 2015
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Hi all. I'm new to the site, just started taking my Computer Architecture course and everything has been going well. Just ran into a problem I can't seem to understand. I looked online and I can't find any help.

So the question is..

A circuit with four inputs A, B, C, D and two outputs X, Y. Now there are 16 different input values from 0 to 15, and they are evenly divided to four parts (0…3; 4…7; 8…11; 12…15), and these four parts match to four output values from 0 to 3. It means that the output value of first four input values is 0, the output value of second four input values is 1, and so on. Please write down the truth table of the circuit, and the logical expressions of the outputs (do not simplify). Then, please draw the circuit, and run it to check the result.

Any help will be appreciated.. Thanks!!

2. ### WBahn Moderator

Mar 31, 2012
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7,653
This is Homework Help, not Homework Done For You.

YOU need to show YOUR best attempt to work YOUR homework problem. We can then see what you are doing right and where you are going off the rails and try to get you back on track.

vlucaj likes this.
3. ### vlucaj Thread Starter New Member

Sep 21, 2015
6
0

This would be everything I have along with the given truth table values. Sorry if my work is not on par with what is expected...

4. ### vlucaj Thread Starter New Member

Sep 21, 2015
6
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And to Mr. Mod,

I said any help is a appreciated. Meaning even just a push in the right direction. Way to welcome a new member/a new person taking interest in this topic.

5. ### WBahn Moderator

Mar 31, 2012
24,454
7,653
Isn't your circuit supposed to have TWO outputs?

It would go a long way to see what you are doing right and wrong if you provided the truth table you came up with. We are not mind readers.

6. ### WBahn Moderator

Mar 31, 2012
24,454
7,653
How can we give you a push in the right direction when we don't know where you are starting from. If you are trying to get to Chicago and I think you are starting from Los Angeles but you are really starting from New York, the push I give you will only send you over your head in the ocean.

Sinus23 and absf like this.
7. ### vlucaj Thread Starter New Member

Sep 21, 2015
6
0
This is what I have so far, I know that the circuit posted above is not correct. It would need two outputs. I'm thinking that when I create a circuit it will need 4 AND gates to begin. That's about where I'm at.

In the question where it says, the output value of first four input values is 0, the output value of second four input values is 1, and so on. What does the so on mean?

8. ### ScottWang Moderator

Aug 23, 2012
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What are the rest output from 4 ~15?

9. ### shteii01 AAC Fanatic!

Feb 19, 2010
4,667
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It means that when you have inputs from 0000 to 0011, the XY are 00 (decimal 0). So your table is wrong, you have XY 01, it should be 00.

For the inputs from 0100 to 0111 the output XY will be 01 (decimal 1).

The next output is XY 10 (decimal 2).

The first four inputs produce decimal 0, next four inputs produce decimal 1, next four inputs produce decimal 2, last four inputs produce decimal 3.
Do you see the logic/system?

10. ### WBahn Moderator

Mar 31, 2012
24,454
7,653
Since you don't have a complete truth table, it means that you don't understand the problem yet. Consequently, you are no where near the stage to even begin thinking about what you might or might not need to solve a problem you don't yet understand.

So let's work on the "understand the problem" phase. By the way, this is the hardest and most challenging phase of most real-world engineering and many engineers do not devote nearly enough effort to this phase of problem solving.

It states that the two outputs form output values from 0 to 3. That means that your outputs are taken to be a two bit binary number. Similarly, the four inputs are taken to represent a four-bit binary number with values ranging from 0 to 15.

11. ### vlucaj Thread Starter New Member

Sep 21, 2015
6
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I think I got it!

12. ### panic mode Senior Member

Oct 10, 2011
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your X and Y just A and B so no circuit is needed

13. ### WBahn Moderator

Mar 31, 2012
24,454
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I was hoping he might have the opportunity to spot that himself, either by inspection or as the result of turning the crank.

14. ### vlucaj Thread Starter New Member

Sep 21, 2015
6
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I understand that its just A and B. But the question said not to simplify.

All set here. Thanks.

15. ### WBahn Moderator

Mar 31, 2012
24,454
7,653
Ah, so it does. Glad you got it and I'm pretty confident you understand it, too.