Problem with digital electronic

Thread Starter

Beginner0001

Joined Sep 29, 2017
13
I need to make mod-12 asynchronous down counter using T flip flop. It counts from 15 to 4. I don't know really how to do it and it's really important, so if you could help me i would be very grateful!
Thank you
 

dl324

Joined Mar 30, 2015
10,536
Welcome to AAC!

For homework, you need to show your best effort before members can try to guide you to a solution.
I need to make mod-12 asynchronous down counter using T flip flop.
Are you certain you're supposed to design an asynchronous counter?
 

crutschow

Joined Mar 14, 2008
24,745
Do you know what a T flip-flop is?
Do you know what a mod-12 counter does?
We need to know your basic understanding level of what you need to do.
 

Thread Starter

Beginner0001

Joined Sep 29, 2017
13
I know what T-ff is and i i kinda understand what mod-12 counter does, but not completely. Like i understood that means that i need to reset counter when it gets to 12, so it can start from begining. I hope you understand what i'm trying to say.
 

dl324

Joined Mar 30, 2015
10,536
Like i understood that means that i need to reset counter when it gets to 12, so it can start from begining. I hope you understand what i'm trying to say.
That isn't what you said in your first post. You said mod-12, but it starts at 15 and counts down.
 

WBahn

Joined Mar 31, 2012
25,578
I know what T-ff is and i i kinda understand what mod-12 counter does, but not completely. Like i understood that means that i need to reset counter when it gets to 12, so it can start from begining. I hope you understand what i'm trying to say.
Your initial post says that your mod-12 counter is supposed to count from 15 to 4. The "mod-12" merely indicates that it has 12 states that it cycles through. The "15 to 4" tells you what those 12 states are, namely

15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 15, 14, 13, ....

There are many ways to approach this. Perhaps start with what you likely already know.

If you were asked to design an asynchronous up-counter that went from 0 to 14, could you do that?
 

Thread Starter

Beginner0001

Joined Sep 29, 2017
13
Oh, that was confusing to me, i think i understand it little better now.

So, counter has to start at 15, then count down to 4. When it gets to 4 then needs to be reset. Am i right?

Can i draw a truth table and send it so you can tell me is it right?
 

WBahn

Joined Mar 31, 2012
25,578
Oh, that was confusing to me, i think i understand it little better now.

So, counter has to start at 15, then count down to 4. When it gets to 4 then needs to be reset. Am i right?

Can i draw a truth table and send it so you can tell me is it right?
Before you start doing truth tables, you need a state diagram and, from that, a state transition table.

Your state diagram needs to reflect the basic approach you have chosen to take. Like I said, there are several viable approaches.

Don't send it to me, post it here.
 

xxxyyyba

Joined Aug 7, 2012
289
I need to make mod-12 asynchronous down counter using T flip flop. It counts from 15 to 4. I don't know really how to do it and it's really important, so if you could help me i would be very grateful!
Thank you
I think that this is explained in every Digital electronics book. There are some steps which you need to follow and that's it. It is explained very well in Digital Fundamentals by Thomas Floyd for example. Roughly speaking, you draw state diagram first, then you write transition table for T flip flop (every flip flop has its own transition table) and after that you have enough informations to fill k-maps, which are necessary to find logical connections between flip flops which make counter. Design procedure is always same, regardless of flip flop type used. So once when you are familiar with design using T flip flops for example, you can design using other types of flip flops also.

I don't think that someone will write step by step tutorial in detail about complete process of counter design. That is because homework section is not meant to function like that. Consult some Digital electronics book or web, there is probably a lot of informations about this online. Then, when you are completely familiar with counter design process, if you stuck somewhere you come here :)
Best regards
 

WBahn

Joined Mar 31, 2012
25,578
You have two columns labeled "Q3". Why? How is a reader supposed to know what Q3 is when you have different values for it? Don't make people guess.
 

Thread Starter

Beginner0001

Joined Sep 29, 2017
13
The second one represents down counting, the first one is there just to make the other clearer. So important part of table begins with second Q3.
 

WBahn

Joined Mar 31, 2012
25,578
If I understand you correctly, the first group is for the current state and the second group is the next state?

If so, then you are saying that from State 15 you are going to go to State 4. Is that what you want?
 

WBahn

Joined Mar 31, 2012
25,578
Your table has several errors:
View attachment 136405
Sure looks like you're doing a synchronous design to me...
The state transition table doesn't really indicate whether it is synchronous or asynchronous. You could draw up a table for a ripple binary counter and it would look the same as the table for a synchronous binary counter. Where the different come in is what comes next -- the excitation logic. For a synchronous design you craft the logic for the control inputs of the FF, for an asynchronous design you craft the logic for the clock (and/or asynch set/reset inputs). Therein is where the demons lay in wait.

If he REALLY needs to do this asynchronously, I would recommend making a simple mod-12 ripple up counter and then decode the outputs to get the desired sequence.
 
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