# circuit design help

Discussion in 'Homework Help' started by zaidsh, Apr 20, 2015.

1. ### zaidsh Thread Starter New Member

Apr 20, 2015
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I need a help on several points in my design, well the design is like this :

1.(input two numbers) *2

2.
if c = 0 ---> input1 + input2
if c = 1 ---> input1 - input2

3. output the bigger number of the two inputs.

please someone help me because this subject is really hard for me and i'll lose my scholarship if I get low grades on this subject! if you don't want to do the whole design just tell me what should I do I'll lookup the steps, thanks!

2. ### shteii01 AAC Fanatic!

Feb 19, 2010
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I am missing the design part.

3. ### zaidsh Thread Starter New Member

Apr 20, 2015
12
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that's the problem I don't know how to start it...

Feb 19, 2010
3,963
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5. ### WBahn Moderator

Mar 31, 2012
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What kind of circuit are you supposed to be designing? Where do these inputs come from? How is the output handled? What is this parameter 'c' and where does it come from?

6. ### zaidsh Thread Starter New Member

Apr 20, 2015
12
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I'm using a software called logisim, You input two numbers (A1A0, B1B0) using pins, and another pin called C , if C = 0 then its A1A0 + B1B0, if C= 1 then its A1A0 - B1B0, and then when we get the result we multiply it by two, and the circuit should also determine the bigger number (A1A0 OR B1B0).

I'm guessing adders and subtractors and comarators, yet I don't know what else to use OR how to effeciently use them.

7. ### WBahn Moderator

Mar 31, 2012
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So how could you use a 2-bit full adder to implement subtraction in response to a control signal?

If you have a subtractor, how can you determine which of two numbers is bigger?

8. ### zaidsh Thread Starter New Member

Apr 20, 2015
12
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I cant answer the first one but the 2nd I'd say before we do the arithmatic operation we compare

9. ### WBahn Moderator

Mar 31, 2012
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So how do you do the compare?

If I have two numbers, A and B, there is an arithmetic operation that I can perform that will trivially allow me to state, based on the result of that operation, whether A>B, A<B, or A=B. What operation is that?

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10. ### zaidsh Thread Starter New Member

Apr 20, 2015
12
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using the comparator?

11. ### WBahn Moderator

Mar 31, 2012
20,215
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A comparator is not an arithmetic operation. Think addition, subtraction, multiplication, and division.