# Need help on a logic circuit - logisim (or any simulator)

#### grllhst

Joined Oct 4, 2021
11
Hello everyone, I'm new here.
So I've got this assignment that asks me to use JK flip-flops in order to create a circuit that obeys the following truth-table:

The thing is, I have no idea on how to get these results at all. From what I understand, first two lines imply that PRE and CLR are both activated on HIGH, but the rest of the lines imply they are activated on LOW. How would I achieve this? Any help would be greatly appreciated.

#### ericgibbs

Joined Jan 29, 2010
19,017
hi grl,
Welcome to AAC.
Look thru this PDF datasheet, ask if you have a query.
Page #2.
E

#### Attachments

• 381.6 KB Views: 11

#### grllhst

Joined Oct 4, 2021
11
hi grl,
Welcome to AAC.
Look thru this PDF datasheet, ask if you have a query.
Page #2.
E
Thank you for responding so quickly! I've read the datasheet, and I think I understand a bit what's happening.
Correct me if I'm wrong but from what I understand I need to use 2 JK flip-flops with synchronous state changes.
However, even if I understood correctly, the truth table I need is still a little bit different from this one (this is what's confusing me the most). My truth table seems to be almost "flipped" comparing to the one on the document and I have no idea on how to achieve that.

#### grllhst

Joined Oct 4, 2021
11
Thank you for responding so quickly! I've read the datasheet, and I think I understand a bit what's happening.
Correct me if I'm wrong but from what I understand I need to use 2 JK flip-flops with synchronous state changes.
However, even if I understood correctly, the truth table I need is still a little bit different from this one (this is what's confusing me the most). My truth table seems to be almost "flipped" comparing to the one on the document and I have no idea on how to achieve that.
Also, If both flip-flops are independent, which one is the correct output for the system?

#### ericgibbs

Joined Jan 29, 2010
19,017
hi grl,
Checking the regular JF F/F IC's , indicates that the Truth table is a little unusual.

I've got this assignment that asks me to use JK flip-flops in order to create a circuit that obeys the following truth-table:

Can you post the full details for the assignment.?

E

#### grllhst

Joined Oct 4, 2021
11
hi grl,
Checking the regular JF F/F IC's , indicates that the Truth table is a little unusual.

I've got this assignment that asks me to use JK flip-flops in order to create a circuit that obeys the following truth-table:

Can you post the full details for the assignment.?

E
Thing is, these are all the details about it. I'll post what it asks, verbatim:
"From the JK flip-flop on logisim and other components on the simulator (extra libraries are not necessary), create a circuit that behaves according to the following truth table."

My main issue here is the truth table that doesn't make too much sense to me. Another possibility is the table is simply incorrect, I'll check that with the professor later today. If the table is indeed correct, I don't even know where to start.

#### grllhst

Joined Oct 4, 2021
11
Thing is, these are all the details about it. I'll post what it asks, verbatim:
"From the JK flip-flop on logisim and other components on the simulator (extra libraries are not necessary), create a circuit that behaves according to the following truth table."

My main issue here is the truth table that doesn't make too much sense to me. Another possibility is the table is simply incorrect, I'll check that with the professor later today. If the table is indeed correct, I don't even know where to start.
To further clarify, I can use any other components on logisim, but the usage of JK flip-flops are mandatory.

#### ericgibbs

Joined Jan 29, 2010
19,017
hi grl,
That 'and other components on the simulator' information makes a big difference.
The way it initially read was that you had to use JK's to make the circuit.

Post what you have on the simulator circuit and I will duplicate using LTSpice.

As this is Homework we can only give hints, not full answers.
E

#### grllhst

Joined Oct 4, 2021
11
hi grl,
That 'and other components on the simulator' information makes a big difference.
The way it initially read was that you had to use JK's to make the circuit.

Post what you have on the simulator circuit and I will duplicate using LTSpice.

As this is Homework we can only give hints, not full answers.
E
By other components it means every basic gate (NOT, AND, OR, etc), plexers, arithmetic components. Basically every component is at disposal.
As this is Homework we can only give hints, not full answers.
This is absolutely fine, any hints given are appreciated. As I said, I have not even a single clue on where to start, so even that would be of great help!

#### grllhst

Joined Oct 4, 2021
11
Post what you have on the simulator circuit and I will duplicate using LTSpice.
What I have is just a simple JK flip-flop. I was so confused with the truth table that I went to study more about it before actually trying anything on the simulator. I know it probably doesn't help too much as I don't really have anything, but that's what I got so far.

#### ericgibbs

Joined Jan 29, 2010
19,017
hi grl,
A cursory scan of the assignment shows it is not a simple task
Which course are you studying and the year.?

E

#### grllhst

Joined Oct 4, 2021
11
hi grl,
A cursory scan of the assignment shows it is not a simple task
Which course are you studying and the year.?

E
Computer Engineering, 5th year. I know it's not a simple task but the more I think about it, the more I think the truth table is incorrect. I'm gonna clarify that before attempting to solve it.

#### ericgibbs

Joined Jan 29, 2010
19,017
hi grl,
A good idea to check that Table, I will wait for your update.

E

#### RBR1317

Joined Nov 13, 2010
715
The way I read the assignment is that you are to create a 'modified' JK FF by taking a standard JK FF and gating the inputs ( and maybe the outputs) to create the behavior specified in the table for the 'new' JK component.

#### grllhst

Joined Oct 4, 2021
11
The way I read the assignment is that you are to create a 'modified' JK FF by taking a standard JK FF and gating the inputs ( and maybe the outputs) to create the behavior specified in the table for the 'new' JK component.
That's exactly it, I was having issue with the truth table, it was very confusing at first but after clarifying with my professor I was able to do it and it is painfully easy lol.

#### grllhst

Joined Oct 4, 2021
11
hi grl,
A good idea to check that Table, I will wait for your update.

E
So after clarifying, I was able to come up with the final circuit:

If you simulate that, you'll notice that it behaves exactly like it should from the truth table. I'm actually very embarrassed that I haven't noticed it was THAT easy. But as they say, there is no such thing as a dumb question. Thank you for the help!

#### ericgibbs

Joined Jan 29, 2010
19,017
hi grl.
As it is a Simulation question, I read the assignment, as that a Simulation had to show a cycle thru the Truth table values.

Actually what you have posted is not a simulation, but a static model of a modified JK F/F,
as post #14 explains.

E

#### grllhst

Joined Oct 4, 2021
11
hi grl.
As it is a Simulation question, I read the assignment, as that a Simulation had to show a cycle thru the Truth table values.

Actually what you have posted is not a simulation, but a static model of a modified JK F/F,
as post #14 explains.

E
Yeah that was it. All we had to do is come up with the static circuit that obeys the table and manually input the values to evaluate. Really sorry about the confusion.