# Logic Gate Coursework Help

Discussion in 'Homework Help' started by Dansterious, Jul 28, 2016.

1. ### Dansterious Thread Starter New Member

Jul 28, 2016
3
0
Greetings All,

Okay so this is actually more out of curiosity, given that It's my friend who needs the help and he thinks I'm 100% up to scratch with what I'm supposed to be doing when I'm not, which on reading that myself makes me realise I probably do need the help too.... Anyway! I was hoping some of you could give me some clues as to what to do.

So basically, we are trying to use a program called "Digital Works" to produce a logic gate circuit which utilises a 7-Segment LED display to progress between a total of 8 specific numbers. So say over a period of 8 seconds, a specific number is shown per second until the list is complete and it reverts back to the first number, a cycle basically.

We are using a 3:8 decoder layout, so 3 input and 8 output. The three inputs on this program are called "sequencers" which are basically bit generators.

What I would like to be explained to me is how I'm able to calculate and design the circuit so that the numbers I wish to be displayed, are so. I appreciate that you may ask why I can't consult the coursework brief or other course media for insight into how to do this, however I have done so and I've found there to be a significant lack of sufficient data to properly explain the process, at least in a way which I am able to fully understand and implement. Additonally, our tutors are currently on leave as Uni is out for summer, so I can't really communicate with them either.

Your help will be greatly appreciated and I'll be happy to provide any further information you may require.

2. ### MrChips Moderator

Oct 2, 2009
12,624
3,451
Welcome to All About Circuits. Hopefully you have come to the right place and I trust you will find the information here to be very useful.

Firstly, let us make sure we understand your problem:

1) You have a single seven-segment LED display.
2) You wish to display a sequence of eight numerals that are non-repeating, e.g 8-3-5-1-0-9-7-4-8-3-5-1...

This is a classic design exercise in a first-year digital logic course.
Note that the numerals do not repeat within the cycle.

There are two additional possibilities that complicate the problem:

1) Numerals repeating in the same cycle, e.g. 8-3-5-8-1-0-9-7...

2) Numerals repeating in succession, e.g. 8-3-5-5-1-0-9-7...

We will not tackle these two additional cases.

The solution entails using flip-flops, (D-type, J-K etc.) in a design known as a finite state machine.
This has been covered numerous times on AAC. Here is one example.

This is also covered in the ebook section of AAC (under the Education tab):

Sequential Circuits:Finite State Machines

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3. ### Dansterious Thread Starter New Member

Jul 28, 2016
3
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Thank you, I appreciate your fast and detailed response. I apologise If I've touched on a subject that has already been frequented on here, I just wasn't sure what to search, to be frank, what I was really looking for. I've had a good look at the links you noted and besides the latter being quite something to get my head round I definitely see how they apply to what I'm doing. The issue is though, I am still having some problems understand where to start with all this.

Perhaps It would make sense If I just attach a picture of the template version of the logic gate circuit which was provided to us by our tutor, which from the looks of it was fairly rushed so you'll have to excuse its crossed nature (You'll see what I mean) aha.

4. ### Dansterious Thread Starter New Member

Jul 28, 2016
3
0
*NOTICE*

I have just realised a fundamental mistake on my behalf which has completely resolved my entire understanding of this task. I didn't realise the bit generators/sequencers could be set to specific intervals so my circuit was always basically without any kind of clock. No wonder I had no idea what I was doing.

Worries Over! Phew.

Thanks for your response, once again. Much Appreciated!

5. ### MrChips Moderator

Oct 2, 2009
12,624
3,451
What I have described is a sequential circuit that includes an element of time, hence the name time state machine.
The diagram you have provided in post #3 is a combinational circuit and the result is independent of time.
In a nutshell, what you want is a 3-bit to 7-segment decoder. You present it with a 3-bit input which you map into any kind of character you desire given 7 LEDs.

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6. ### CaptainQuantum New Member

Jul 28, 2016
1
1
I actually personally had a similar question except I was thinking of LEDs. I wanted to light them up in order. Here's a schematic I made to light one up at a time at when Clk is 2 Hz per second. Link

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