# Need help with understanding a 7 segment display with 3 inputs(A,B,C)

#### pokin

Joined Jun 20, 2019
8
Hi everyone I’m currently a first year student and I need some help. In the picture I have attached, it says that when CBA=0 the 7 segment display will show the letter E, can someone explain why? And what are the possible letters for the other CBA combinations, thanks everyone

#### MrChips

Joined Oct 2, 2009
27,711
Welcome to AAC!

There is no "why".

When CBA = 000, display "E".

For the rest of the assignment, you are challenged to think outside of the box.
That is what a good engineer does.

#### pokin

Joined Jun 20, 2019
8
Welcome to AAC!

There is no "why".

When CBA = 000, display "E".

For the rest of the assignment, you are challenged to think outside of the box.
That is what a good engineer does.
Hi, does that mean that there are many possible displays for 001?

#### djsfantasi

Joined Apr 11, 2010
8,682
Hi, does that mean that there are many possible displays for 001?
Who knows? The problem isn’t about any other value for CBA than 000.

Why would you think that there are many possible displays for CBA equal to 001?

It’s not relevant.

#### pokin

Joined Jun 20, 2019
8
Who knows? The problem isn’t about any other value for CBA than 000.

Why would you think that there are many possible displays for CBA equal to 001?

It’s not relevant.
Sorry, I’m starting to think I don’t understand the diagram at all, are A,B,C switches that control abcdefg? If so, how many letters is one switch controlling? Sorry if I seem really clueless because I am, thanks

#### AlbertHall

Joined Jun 4, 2014
12,190
What is the 'Table 1 below' that is mentioned but doesn't seem to be included above?

#### pokin

Joined Jun 20, 2019
8
That would be table 1

#### djsfantasi

Joined Apr 11, 2010
8,682
Sorry, I’m starting to think I don’t understand the diagram at all, are A,B,C switches that control abcdefg? If so, how many letters is one switch controlling? Sorry if I seem really clueless because I am, thanks
It’s explained in the first image of the problem statement.

A,B,C are digital inputs. They may come from a variety of sources. Another digital circuit perhaps? Or maybe some switches.

What we know is that each input represents either a ‘1’ or a ‘0’. If it helps you visualize the problem, sure, you can think of them as switches.

Do not think that a switch controls segments directly! What classes have you taken that covers digital logic? Do you know what a “logic gate” is? An AND? Or an OR? Even a NOT?

The input “controls” a-g as far as their values are processed by the “Digital Logic Circuit” in the problem statement. That unknown circuit (which is what you need to design to answer the problem) takes the inputs and lights the necessary segments in such a way that an input of 000 displays the letter ‘E’ on the 7-segment display.

Nothing further.

#### pokin

Joined Jun 20, 2019
8
It’s explained in the first image of the problem statement.

A,B,C are digital inputs. They may come from a variety of sources. Another digital circuit perhaps? Or maybe some switches.

What we know is that each input represents either a ‘1’ or a ‘0’. If it helps you visualize the problem, sure, you can think of them as switches.

Do not think that a switch controls segments directly! What classes have you taken that covers digital logic? Do you know what a “logic gate” is? An AND? Or an OR? Even a NOT?

The input “controls” a-g as far as their values are processed by the “Digital Logic Circuit” in the problem statement. That unknown circuit (which is what you need to design to answer the problem) takes the inputs and lights the necessary segments in such a way that an input of 000 displays the letter ‘E’ on the 7-segment display.

Nothing further.
Can it be said that there only 3 logic gates in this “unknown circuit” and each logic gate has 3 inputs?

#### djsfantasi

Joined Apr 11, 2010
8,682
No...

Are you guessing?

You never answered my question. What courses in digital logic have you taken or are taking?

#### pokin

Joined Jun 20, 2019
8
No...

Are you guessing?

You never answered my question. What courses in digital logic have you taken or are taking?
Digital electronics?

#### djsfantasi

Joined Apr 11, 2010
8,682
Digital electronics?
Is that a question or statement?

Digital electronics is a start. It builds on an understanding of digital logic. Either as a separate study or as the first few sessions of a digital electronics course.

Explain please, where or how you got the idea that you’d need three logic gates with three inputs? Perhaps if I understood your explanation, I can guide you better.

#### pokin

Joined Jun 20, 2019
8
Is that a question or statement?

Digital electronics is a start. It builds on an understanding of digital logic. Either as a separate study or as the first few sessions of a digital electronics course.

Explain please, where or how you got the idea that you’d need three logic gates with three inputs? Perhaps if I understood your explanation, I can guide you better.
It was a statement, the question mark wasn’t intentional.

It says on the paper that A B C are digital logics with 3 input and I assume A B C are in the digital logic circuit and theres also 3 inputs going into A B C I assume thats stated on the block diagram

#### djsfantasi

Joined Apr 11, 2010
8,682
No, it says that

A,B, & C are symbols that represent a 3 input digital logic.​

I can see how the language is confusing. But this is how I read it.

A,B,C are symbols that represent - 3 inputs to a digital logic circuit.​

#### pokin

Joined Jun 20, 2019
8
No, it says that

A,B, & C are symbols that represent a 3 input digital logic.​

I can see how the language is confusing. But this is how I read it.

A,B,C are symbols that represent - 3 inputs to a digital logic circuit.​
Am I right to say that what I drew is correct? In terms of what A B C is( ignore the “AND”)

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#### BobTPH

Joined Jun 5, 2013
6,086
You were asked to design a digital logic circuit that has 3 inputs and 7 outputs. Does what you drew correspond to that?

Bob

#### djsfantasi

Joined Apr 11, 2010
8,682
Let’s assume that what you drew is correct (I don’t think it is). Then, how would you determine what to display if the input is 001? Or 010, 011, 100, 101, 110, 111?

Start with what you posted and figure out what is needed for all of the other combinations. If you find that you need to modify your first answer, then do so.

Another hint. What is the output of the AND gate, in what you proposed, when the input is 001? (when does an AND gate output a 1?). Does the problem allow for the 7-segment to be an E if the input is anything but 000?