Under which input condition, the J-K Flip-Flop toggles ?
J = 1, K = 1
The whole point of the J-K flip-flop is that it turns the forbidden state of the S-R flip-flop into a useful one. Its characteristic table reads:
| J | K | Qn+1 | Action |
|---|---|---|---|
| 0 | 0 | Qn | No change (hold) |
| 0 | 1 | 0 | Reset |
| 1 | 0 | 1 | Set |
| 1 | 1 | \(\overline{Q_{n}}\) | Toggle |
So the toggle condition is J = K = 1, option 4.
The characteristic equation summarises all four rows in one line:
\(Q_{n+1}=J\overline{Q_{n}}+\overline{K}Q_{n}\)
Substituting J = K = 1 gives \(Q_{n+1}=\overline{Q_{n}}\) directly.
How the toggling is achieved internally. A J-K flip-flop is an S-R flip-flop with the outputs cross-coupled back to the input gates:
\(S=J\overline{Q}\qquad R=KQ\)
When J = K = 1, exactly one of these is active at any moment — whichever one changes the state — so the invalid S = R = 1 condition can never arise. That feedback is also the origin of the race-around problem: with a level-triggered clock and a pulse width longer than the propagation delay, the output would toggle repeatedly within a single clock pulse. The cure is edge triggering or the master-slave arrangement, in which the master responds while the clock is high and the slave transfers the value only when it goes low, guaranteeing exactly one toggle per clock.
Where the toggle mode is used. Tying J and K permanently to 1 makes a T flip-flop, which divides the clock frequency by two — the basic cell of every ripple counter and frequency divider.
Hence, the flip-flop toggles when J = 1, K = 1.
Similar Questions
The truth table of D flip-flop is given below:
C D Qn+1 O X Qn (Last State) $\uparrow$ 0 0 $\uparrow$ 1 1 Choose exact characteristic equation based on above Truth Table
Assertion (A) : Delay flip flop is used to store a single bit either 0 or 1.
Reason (R) : It has only one input, when clock is high and D input is also high, the output resets.
Assertion (A) : Asynchronous sequential circuit is also called event driven circuit.
Reason (R) : Event driven circuit does not have clock to trigger change of state. The states are changed by the change in input signal of the previous stage.
Select your answer using the codes given below.
For the circuit shown below consider the two statements :
Assertion (A) : The circuit is sequential.
Reason (R) : There is a loop in circuit.
Select your answer using the codes given below.
Flip Flop can be used to make :
(a) Latches
(b) Bounce-elimination switches
(c) ADDER
(d) Encoder
Which of the statements given above are correct ?
Read the following statements :
(a) In a J-K Flip Flop, if J = K, the resulting Flip Flop is referred to as a T-type Flip Flop
(b) In a J-K Flip Flop, if J ≠ K, the resulting Flip Flop is referred to as a D-type Flip Flop
(c) An S-R Flip Flop cannot be converted into a T-type Flip Flop since S = R = 1 is not allowed.Which is correct ?
Which of the following statements are true regarding the operation of JK flip-flop ?
1. When K input is low and J input is high, the Q output of the flip flop is reset.
2. When K input is high and J input is low, the output Q of the flip flop is set.
3. When both the inputs K and J are low, the output Q does not change.
4. When both the inputs K and J are high it is possible to set or reset the flip-flop (ie) the output toggle on next positive clock edge.Which one of the following is true ?
Assertion (A) : D-flip-flops are used as buffer register.
Reason (R) : Flip-flops are free from "race-around" condition.
Select your answer using the codes given below :
In the circuit shown below, the output Y1 and Y2 for the given initial condition Y1 = Y2 = 1 and after four input pulses will be
Read the following statements :
i. Gate is a combinational logic.
ii. JK Flip-flop in toggle mode is not combinational logic.
iii. MSJK FF suffers from race-around.
iv. Counters are sequential circuits.Which is correct ?
Important Questions from Sequential Circuits
A basic memory storage element in a digital system is:
The basic sequential logic building block in which the output follows the data input as long as the ENABLE input is active, is
What can be the maximum clock frequency of a 10-bit ripple counter which will not cause a count to skip, considering 10 ns propagation delay for each of the edge-triggered flip flops?
The output of a sequential circuit depends on
The basic building block of a sequential logic circuit is
