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Making a J-K flip flop from a D-Type Flip Flop

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Terabyte

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Hey

I understand you can make a D-Type Flip Flop from a J-K flip flop by attaching J to K and inverting J...

But a past paper I have here is asking for it to be done the other way round?

"Design a circuit for the J-K flip flop using one D-Type flip flop and whatever other gates you require"

Any Help much appreciated thanks.
 
Terabyte said:
Hey

I understand you can make a D-Type Flip Flop from a J-K flip flop by attaching J to K and inverting J...

But a past paper I have here is asking for it to be done the other way round?

"Design a circuit for the J-K flip flop using one D-Type flip flop and whatever other gates you require"

Any Help much appreciated thanks.

Well I can think of two ways you can approch this exercise.

1. Draw out the truth table of a JK and figure out the external input gating you would need to driving a type D FF as the output device.

2. It's probably more educational to just study the difference of these two types of FFs using their gate equivelent logic drawings from their data sheets:

page 3 of https://www.electro-tech-online.com/custompdfs/2007/04/sn7473.pdf shows a gate equivlency of a JK FF.

page 1 of **broken link removed** shows a gate euivlency of a type D FF.

good luck

Lefty
 
A JK flip-flop can do four things. It can set, clear, toggle and hold. Sounds like a four input multiplexer with J and K as select lines, and the inputs wired to one, zero, Q-bar, and Q.
 
Papabravo said:
A JK flip-flop can do four things. It can set, clear, toggle and hold. Sounds like a four input multiplexer with J and K as select lines, and the inputs wired to one, zero, Q-bar, and Q.

That did it for me:)

Thanks
 
I hate to bring this thread back up after such a long time, but I'm in a few digital design classes this semester and was looking for information when I noticed this thread.

First, Papabravo is correct, you can implement a JK from a D if you simply use a multiplexer. However, if you're doing this in a company or test setting, you may not be able to use a multiplexer and might wonder how you can do this with minimal logic.

So, the basic idea with converting any flip flop into another is to map different inputs around until you get the right mapping going. You can easily do this using a K map.

For example, here you would use a K map with three variables Q, J, and K. You can then say, for example "when Q = 1 and J and K are also 1, the input to D should be 0," or likewise.

This is actually kind of similar to how you build state machines, sequencers, etc... by hand. The main idea is to look what states map to what inputs and outputs, put them on a K map, design the glue logic, and go about implementing them.

I think that is correct, I can provide a full example on how to design any flip from (SR, JK, T, D, etc...) from any other if anyone has any questions.

-- Kris
 
I think that is correct, I can provide a full example on how to design any flip from (SR, JK, T, D, etc...) from any other if anyone has any questions.

-- Kris

Hi, sorry to bring this up after so long again. Kris: Would you still be willing to provide a full example on how to design a JK flip flop FROM a D flip flop and any other logic gates necessary with minimal logic? Thank you.
 
Just don't forget that you MUST include a clocked element (the D F/F) for the edge triggering and that you must invert the clock input since all JK flip flops are negative-edge triggered and all D flip flops are positive-edge triggered.
 
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