About Positive Edge Triggered FF J-K Flip-Flop

[_q12x_]

• I am thinking on buying a couple of Positive Edge Triggered J-K FF Flip-Flop.
• Who do you recommend? Who is the Best?
• Or, what did you used so far and from your experience is good enough or super good to use?

Mister @marconi ? or anyone else?
Thank you.
-----------
Heh, nevermind - I buy already this 74LS76
---also, is impossible to delete this thread; hahahahahaha

 

[marconi]

The 74LS76 is a good one to buy and has the nice features of 'Preset' and 'Clear' which means you can preload 4 bits of data to appear at the Q outputs eg 1010, and clear the Q outputs to 0000 as you are familiar with already.

I recommend you study the datasheet and in particular the the Function Table.

https://www.ti.com/lit/ds/symlink/sn5476.pdf?ts=1665145059568&ref_url=https%3A%2F%2Fwww.google.com%2F

PS: I think I may have a few of these too.

 

[_q12x_]

This is the context I was very specific about being "Positive Edge Triggered" J-K FF Flip-Flop
At some point of the development of that 8bit computer, actually I believe it was in the very start of it, I encounter a very big problem where I was trying to use this circuit using diodes instead of a AND or 2 NAND gates. That you actually solved the problem, because it didnt worked with a single AND gate either.
The problem was my CD4027 was too fast and the diodes and the AND gate was not registering the pulse.

This is the solution that my american friend from the other forum come to:

I just tried Jony130's circuit above with both the CD4027 and a 74LS74 D Type flipflop. The CD4027 doesn't work because the reset pulse is way too fast to trigger it, but the 74LS74 DOES manage to trigger properly, and switch the LED on and off.

and then ...
-

---
q12x said: I just look now in my IC list and I dont have your 74LS74. But Im glad it worked, with a special FF then, that was the answer. VERY interesting !!!! Really - thank you !
---
If you have any Positive Edge Triggered 74LS series flipflop IC's in your list, try one of those instead of the 74LS74. Should work!

And I looked into my list and all I have is a 74HCT73 Negative Edge Triggered IC. Haha. And I think only 1pcs. I imagine I can do a trick or 2 with it and make it work as a Positive, most probably with a NOT gate on its inputs...
But I love the idea of having the freedom and the possibility of including diodes and make discrete gates with working FF next time. This is the reason.
I hope now is clear.

 

[_q12x_]

I believe I made a mistake.
I believe I also bought a Negative Edge Triggered IC. Aaaaah. And now I see it.
SN74LS76AN

When they say 'LS76A I believe they refer to this sector SN74LS76AN from the name. Correct?
Im so screwed.

 

[marconi]

I forgot to mention it at the time but now I will now for your interest and amusement. The Resistor-Diode logic has the major drawback that using ordinary diodes it is very slow and thus cannot function with very short duration pulses such as the reset pulse. You may be surprised to know that a diode also has capacitance between the anode and cathode named in its equivalent circuit as the diffusion capacitance. The value of this capacitance depends on whether the diode is forward or reversed biased and by how much. The capacitance changes inversely with reverse bias and grows as the reverse bias is reduced towards zero and the biasing becomes forward. This means the forward biased diode takes longer to turn off than it takes for it to turn on from the reversed biased state. These recovery times - see attached article - limit the speed at which the diodes in diode-resistor logic are able to process fast and short pulses which switch between logic 1 and logic 0. Some types of diode are faster to switch on and off eg: Schottky and Tunnel. The 74LS series uses Schottky diodes.

There is another effect which slows down a diode's ability to switch and this is to do with the finite time it takes for the charge carriers - electrons and holes - to actually move in the semiconductor.

AC Equivalent Circuit of Semiconductor Diode | Reverse Recovery Time - https://www.eeeguide.com/ac-equivalent-circuit-of-semiconductor-diode/

 

[marconi]

_q12_x: What project do you have in mind next? And did you ever fit those wings to your illuminated wings proximity switch?

An idea for a project or a novel present for someone - a tooth brushing timer using a pattern of LEDs to model the layout and the location and edge of a tooth to clean and for how long and maybe a countdown too for the complete activity? Perhaps have some ability to alter durations too.

Tooth and mouth illustrations - https://dentalimplants-usa.com/bone-and-teeth/tooth-and-mouth-illustrations/

My Autumn project is to use one of these RF Solutions 868MHz receiver decoder devices to control our front door lock remotely and to send simple instructions to a visitor from my wife's medical room; and to have another device at the door to send messages back to the medical room if only for the visitor to acknowledge. The EEPROM may come in handy because I have some 7 x 5 led matrix displays to use somehow.

RF Solutions Remote Control Base Station KAPPA-T868, Receiver, 869.5MHz, FM | RS - https://uk.rs-online.com/web/p/remote-control-base-stations/1110161

 

[_q12x_]

Ok, I understand your point with the diodes, I do. But I will still want to use that circuit for my learning curve and also discover myself how much slower they really are comparative with another dedicated chip.
I have 2 questions for you, and I thought they were obvious.
1- I am totally screwed now that I have Negative Edge Triggered IC instead of Positive as I originally wanted?
2-How can I slow down the original FF CD4027, not to switch this fast, to make it compatible for the diodes circuit?
Thank you.

 

[marconi]

deleted message..................................................not sure I have understood the context of your questions.

 

[_q12x_]

deleted message..................................................not sure I have understood the context of your questions.

tell me what is unclear and I will clarify it to you

 

[pc1966]

Why is the -ve clock edge such an issue? Answer is to feed it from and inverter such as the 'LS04 or if the source is slow-edged, to use a Schmitt trigger inverter such as the LS14/HC14/HCT14 (or if you need a NAND gate then ..132 has Schmitt trigger inputs).

Same about the reset pulse, you can stretch those out with R, diode, C and a Schmitt trigger of choice.

 

[_q12x_]

Aaaand I decided. I buy a couple of 74LS74 as well. I know for sure they are Positive Edge Triggered FF.
A bit costly to my pocket, but hey... if it will get the job done, is worth it.
This way I will have all the FF flavors in the world.

 

[marconi]

tell me what is unclear and I will clarify it to you

Why does which edge for triggering bother you at the moment? One of your previous projects?

 

[_q12x_]

oh...it remained as a curiosity of why didnt worked with the diodes ! I want to find the solution of making it work with the diodes, as in the circuit I shown.

 

[_q12x_]

I just remade that circuit just now and still not switching. Here is how I have it right now:
For the 7476 I dont have the original chip. I only --discovered-- that I have a single (1one) CDB476E which is an equivalent. Im not completly sure if the pins are maintained the same. It better be. The D9 LED is ON all the time and not switching when I press the button on CKA of the 7493. Ive also inserted a NOT gate here:

but still no effect. It might be switching still too fast ?!
How can --I-- make it work? Thats the question.

 

[marconi]

You have clarified matters in your latest posts. I thought I had explained why - or at least attempted to - why the diode-Resistor AND gate was unable to function correctly and provide a reset pulse to the 93 with such fast short duration 93 Qx pulses when 0111 is reached. What you are now working on is the problem with the combination of DRL and the FF which toggles the red LED on/off to indicate the reset pulses are there.

As those diode switch off faster than they switch on, and they switch off at 0111, you will be dealing with a reset pulse which transitions 0 to 1 so its leading edge is quicker than its trailing edge. What you require is a circuit to detect the leading edge of the reset pulse and then stretch it long enough to toggle the red led on and off. Try this 7400 circuit first. We can stretch the pulse more later if we need to.

 

[marconi]

I believe I made a mistake.
I believe I also bought a Negative Edge Triggered IC. Aaaaah. And now I see it.
SN74LS76AN
View attachment 102330
View attachment 102329
When they say 'LS76A I believe they refer to this sector SN74LS76AN from the name. Correct?
Im so screwed.

Item numbers for a device really do matter - a good learning point for you. Generally the later numbers and letters of an item number refer to derivative, options or performance for the main device.

 

[_q12x_]

I managed to make it work ! Specifically for 7473 FF ! Read the note for C1 in the bottom of the image.

 

[_q12x_]

I made multiple tests.
Also with your circuit and it does not work.
I also put the osciloscope. It can read the 500ms from the button debounce circuit just fine. But absolutely nothing on the FF clock pin. I tried a lot of time sequence, from 1s to its minimum of 10us. Nothing. I believe this signal MAY be too fast even for my osciloscope to catch it. Thats interesting !!! And I have top of the game osciloscope. Oau.
And I am speacking from the point of view of both FF's. The one that is working with the 7473 and the one that is not working with a 4027.

 

[marconi]

The is a subtle difference between the 7473 and the 7476/4027/7493 flip flops. Whereas 76, 27 and 93 are edge triggered the 73 is level triggered. In my attached electrical art the clock pulse edges are marked 4(leading/positive) and 3(trailing/negative) and the levels are marked in green as 1(Logic 1) or 2(Logic 0).

Briefly, the trigger to change the FF's state is based on detecting when the clock is at either logic 1 or logic 0 for the level triggered FF 7473. The others are triggered when they detect the clock waveform is changing from 0 to 1 ie rising or falling ie 1 to 0.

The 73 uses the logic 1 level. The 76/27/93 use the leading edge; the 76A/27A/93A* use the trailing edge.

I think your C1 is working by being quickly charged by the 1kR - during the brief interval when Qn changes from 111 to 000 - to extend the period of time the Reset signal R is at Logic level 1 so that it is long enough for the 7473 to detect it as such and thence toggle the FF. On becoming 111 the R goes to logic 1 but does not instantaneously drop now to logic 0 at 000 - R has been stretched a tiny bit in time. The 73 data sheet says the minimum time for the clock to be at logic 1 is 20nanoSeconds.

* I am pretty sure there is a 93A which uses the trailing edge but I don't have time right now to confirm that.

 

[pirate]

Just thought I would mention that I am completely out of my depth here! Great to see a discussion between folk who have a completely different knowledge-base from me.
I can, however, make a really nice paella!
Seriously, it's amazing to see stuff that's so different from the norm, and I love this forum for the variety it affords.