# Logic Circuits

Discussion in 'Homework Help' started by gsanjaya, Jan 18, 2016.

1. ### gsanjaya Thread Starter New Member

Jan 18, 2016
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A A nalyse the logic circuit shown in Figure 2. The inputs to the circuit are C0, A0, B0, A1, B1, A2 and B2. The outputs are S0, S1, S2 and C3. The internal structure of the logic block in the middle of Figure 2 is shown in Figure 3.

Mod edit: Moved to Homework Help

Last edited by a moderator: Jan 18, 2016
2. ### Kermit2 AAC Fanatic!

Feb 5, 2010
3,851
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Do you know the truth tables for the various logic gate types shown in your problem?
If you do then start with all inputs at 0 and follow them through to the output. Create another larger truth table for the assignment and list all inputs and outputs.
This one will take a few hours of your time.
If you just want someone to give you answers, then you need to seek for them elsewhere. We are here to help you do it yourself and not to do it for you.

3. ### WBahn Moderator

Mar 31, 2012
18,087
4,917
What is meant by "analyze the logic circuit" in this problem? Are you expected to come up with equations for each of the outputs in terms of the inputs, or would a truth table for the circuit suffice?

If a truth table would be sufficient (which would have 128 rows), then you could construct it pretty quickly in a spread sheet.

If they want equations, then do it is stages. First get equations for the outputs of the boxed circuit in terms of the inputs to the boxed circuit. Then get equations for the inputs to the boxed circuit in terms of the overall inputs. Then get equations for the overall outputs in terms of the outputs of the boxed circuit and inputs to the boxed circuit. Then combine them together.

It shouldn't take too terribly long -- perhaps half an hour or so. There is actually a lot of structure in the circuit that makes it reasonable straightforward.

4. ### dl324 Distinguished Member

Mar 30, 2015
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651
OP resurrected this 5 year old thread that had the same logic diagrams. It included this additional information

5. ### WBahn Moderator

Mar 31, 2012
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Interesting. I was going to ask if they were supposed to figure out a simple description of what it does, such as adding two three-bit inputs A and B, but decided that that would risk running things off on a tangent.

I'm assuming that the circuit is an assignment that is given by some prof periodically. Out of curiosity, how did you spot that prior incarnation?

6. ### WBahn Moderator

Mar 31, 2012
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Never mind -- I see how you spotted it.

7. ### WBahn Moderator

Mar 31, 2012
18,087
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Gee, looks like I even guessed what it does (and it was pretty much a guess that I didn't really think was likely to be correct).

8. ### dl324 Distinguished Member

Mar 30, 2015
3,378
651
I'm curious how the OP found it.

9. ### WBahn Moderator

Mar 31, 2012
18,087
4,917
Good question, though when you read a thread here you get the "Similar Threads" list at the bottom and they are almost always many years old. So they probably did a search and then explored the threads listed at the bottom.

10. ### WBahn Moderator

Mar 31, 2012
18,087
4,917
@gsanjaya : I see that you are only 17 years old, and that is pretty young compared to most people that are learning this stuff. Are you learning this in high school (or whatever the Australian equivalent is) or are you taking college courses?

How comfortable are you with Boolean expressions involving NOT, OR, and AND? Are you comfortable with expressions involving XOR?

11. ### WBahn Moderator

Mar 31, 2012
18,087
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I don't know how reasonable I think it is for a student (or most anyone else) to be able to look at a bunch of low level logic equations and divine what high level conceptual function they implement, so don't feel too bad if it isn't apparent to you. Hopefully this problem was given within a context that really narrows things down. Certainly the choice of names for input and output signals is a pretty big hint.