# Circuit with an integrated FLIP FLOP

#### tnn

Joined Jul 21, 2017
44
Hello everyone,

I have to make a small circuit with an integrated FLIP FLOP that has this function:

1. pin A and B input to 1, pin C output goes to 1
2. when pin A is 1 and pin B is 0, pin C goes to 0 and remains there even if pin B returns to 1
3. pin C returns to 1 only when pin A goes from 1 to 0 and then to 1 again and with pin B to 1

how could I do? Help thanks.

#### MrChips

Joined Oct 2, 2009
23,873
Hello everyone,

I have to make a small circuit with an integrated FLIP FLOP that has this function:

1. pin A and B input to 1, pin C output goes to 1
2. when pin A is 1 and pin B is 0, pin C goes to 0 and remains there even if pin B returns to 1
3. pin C returns to 1 only when pin A goes from 1 to 0 and then to 1 again and with pin B to 1

how could I do? Help thanks.
Sounds like a simple R-S flip-flop. You can use any such as 7474 or just two NAND gates.

#### shortbus

Joined Sep 30, 2009
8,696
Sounds like a simple R-S flip-flop.

Also sounds like homework. Should be moved to that forum?

#### tnn

Joined Jul 21, 2017
44

#### MrChips

Joined Oct 2, 2009
23,873
I had seen it but in my case, when S and R are at 1?
When S and R are at 1 there is no change in state of the flip-flop.

#### tnn

Joined Jul 21, 2017
44
I'll explain:
pin A is set to 1 when the circuit is powered.
Pin B is connected to a thermal switch that keeps pin 1.
When the thermal switch intervenes, pin C must go to 0 and must remain there even if the thermal switch closes again.
Pin C should return to 1 only when power is removed from the circuit and then switched back on and pin B is at 1.

#### MrChips

Joined Oct 2, 2009
23,873
Hah!
Now you have introduced a third condition. POWER-ON RESET.
You have to implement this behaviour explicitly in your circuit. It will not happen on its own.

#### tnn

Joined Jul 21, 2017
44
Can you give me an example of circuit ...

At power on, C goes to 1 if A and B are at 1.
After if B goes from 1 to 0, C goes to 0 and stays there until there is a reset of the circuit….

I hope this is clearer …

Last edited:

#### MrChips

Joined Oct 2, 2009
23,873
Here is a simple POR circuit.

On POWER-ON the output signal /RESET is low.
After approximately RC seconds /RESET goes high. Use a logic gate to combine this with your A signal. You can also use diode logic.

#### tnn

Joined Jul 21, 2017
44
Could I kindly have an example of a circuit to start from?
this is the state diagram

#### MrChips

Joined Oct 2, 2009
23,873
Your state diagram is not correct.
This is homework or assignment of any kind?

#### tnn

Joined Jul 21, 2017
44
no being closed at home I'm dusting old ideas ...

Your state diagram is not correct.
Kindly tell me where is the mistake?

#### tnn

Joined Jul 21, 2017
44
Your state diagram is not correct.
but I reviewed them but for me they are correct ...

However, in the meantime, it made it simpler, that is, with the evergreen NE555 and two transistors ...

What do you think?

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#### iimagine

Joined Dec 20, 2010
483
What do you think?
The 555 is wired as a monostable 'one shot' and thats it.
SW1 does nothing!
SW2 does nothing!

Until you provide a complete truth table, no one will be able to help you. For example, what if A is 0 and B is 0?

#### tnn

Joined Jul 21, 2017
44
SW1 does nothing!
SW2 does nothing!
but when ever! I tried it and it works perfectly ...