# 7 Segment using D-Flip flop (URGENT HELP!)

#### sfthdfghjghjg

Joined Aug 26, 2022
4
Hi,
I need help with writing a state table of 7 segment with 4-bit input A,B, C "Present state", and x "Input".

#### Papabravo

Joined Feb 24, 2006
20,400
Hi,
I need help with writing a state table of 7 segment with 4-bit input A,B, C "Present state", and x "Input".
What does this have to do with flip-flops. Binary to 7 segment is a combinatorial problem, so no state table. Right? I think we need a better description of what you have in mind. A schematic diagram would be great for that purpose.

#### Alec_t

Joined Sep 17, 2013
13,795
Since this is Homework, post your best effort at solving the problem, so that we can give guidance where needed.

#### sfthdfghjghjg

Joined Aug 26, 2022
4
What does this have to do with flip-flops. Binary to 7 segment is a combinatorial problem, so no state table. Right? I think we need a better description of what you have in mind. A schematic diagram would be great for that purpose.
Because we need it to work with 1 Hz frequency. Thus, your
counter will count once per second.

#### sfthdfghjghjg

Joined Aug 26, 2022
4
Since this is Homework, post your best effort at solving the problem, so that we can give guidance where needed.
Since this is Homework, post your best effort at solving the problem, so that we can give guidance where needed.
It should be 3 inputs (A, B, C).
And Output should be in this sequence ( 5-3-7-1-0-4)

#### Papabravo

Joined Feb 24, 2006
20,400
Because we need it to work with 1 Hz frequency. Thus, your
counter will count once per second.
I don't have a very clear picture of what you are describing. With each answer you reveal additional details, but not the complete picture. If you don't have a schematic diagram how about a simple block diagram of what you have in mind, because your words are just not making it clear.
EDIT: I see the diagram -- thanks.

#### Papabravo

Joined Feb 24, 2006
20,400
Your state table looks OK except for the XXX entries in next state column for present states 6 and 2. The X designation usually means don't care, but you don't want to do that. States 6 and 2 are invalid states. The proper treatment of invalid states is to make them go to a legal state, and make the machine is self-correcting. Usually, the best strategy is to make an invalid state valid by changing at most a single bit. You could do this for example by mapping 2 --> 1 and 6 --> 7. The rest of the state table looks fine, but I did not check the logic for the flip-flop inputs.

So, what does this have to do with anything about 7 segment?

#### dl324

Joined Mar 30, 2015
15,842
Since no one else has already done it... Welcome to AAC!
It should be 3 inputs (A, B, C).
And Output should be in this sequence ( 5-3-7-1-0-4)
This is different than what you initially posted. Please post the entire text of the problem and the due date.

From the statements above, it appears that you're to design a synchronous counter that counts 5-3-7-1-0-4. The 3 inputs requirement is misleading. I'd only consider the clock to be an input.

It would be helpful if you posted your Kmaps. What is the counter not doing correctly? Are you certain your table is correct?

Are they teaching you that 'A' should be the MSB? That's backwards from what professionals have been using for the past 50 years or so. A is always the LSB.

From Texas Instruments 1981 TTL Databook:

#### dl324

Joined Mar 30, 2015
15,842
It appears that you checked your thread and didn't feel like answering any questions. I'll tell you that your table has an error.

The don't cares are fine as long as the problem didn't give some requirement for how quickly the circuit needed to count out of invalid states. For homework problems, invalid counts are typically treated as don't cares to facilitate simplifying the logic.

In addition to not using 'A' for the LSB, are they not teaching you to put your truth table in gray code order? Using gray code that facilitates transferring data to Kmaps.

Also note that the transition table (I think that's what they call it) for D flip flops is the same as next state.

#### sfthdfghjghjg

Joined Aug 26, 2022
4
It appears that you checked your thread and didn't feel like answering any questions. I'll tell you that your table has an error.

The don't cares are fine as long as the problem didn't give some requirement for how quickly the circuit needed to count out of invalid states. For homework problems, invalid counts are typically treated as don't cares to facilitate simplifying the logic.

In addition to not using 'A' for the LSB, are they not teaching you to put your truth table in gray code order? Using gray code that facilitates transferring data to Kmaps.

Also note that the transition table (I think that's what they call it) for D flip flops is the same as next state.

But, the deadline was yesterday and we got other things to submit with this homework, so me and my team was so busy and stressed to meet the deadline.

Finally, we try our best and the circuit worked fine on the software "proteus" and we submitted it.

Thank you so much my friend!

#### dl324

Joined Mar 30, 2015
15,842
But, the deadline was yesterday and we got other things to submit with this homework, so me and my team was so busy and stressed to meet the deadline.
The way homework help works on AAC is you have to do most of the work and we're only allowed to give you hints. That means urgent requests are doomed to fail.

It's usually the case that the written instructions for a problem will provide more detail than a student's description of the problem. Particularly if they're lost and don't understand the material and end up here asking for help.

If your school is teaching you the form you're using (A is not always LSB, truth tables aren't in gray code order), I think you'd be better off going to a better school. This field is built on the shoulders of giants and those giants said A is always the LSB and gray code order rules.

A member once suggested that there are times when decimal order could be better than gray code. I don't buy it.