The toggle condition appears in J-K flip-flop when A. J=1, K=1 B. J=0, K=0 C. J=0, K=1 D. J=1, K=0 E. J=0, K=1 and J=1, K=0 Choose the correct answer from the options given below :
A only
The J-K flip-flop's four input combinations. Its characteristic equation is
\(Q_{n+1}=J\overline{Q_n}+\overline{K}Q_n\)
which gives the complete excitation table:
| J | K | Qn+1 | Action |
|---|---|---|---|
| 0 | 0 | Qn | Hold (no change) |
| 0 | 1 | 0 | Reset |
| 1 | 0 | 1 | Set |
| 1 | 1 | \(\overline{Q_n}\) | Toggle |
Check the toggle row against the equation. Putting J = K = 1:
\(Q_{n+1}=1\cdot\overline{Q_n}+\overline{1}\cdot Q_n=\overline{Q_n}\)
so the output complements on every active clock edge — that is the toggle condition, i.e. statement A.
Why the other statements are not toggle. B (J = K = 0) holds the previous state; C (J = 0, K = 1) forces a reset to 0; D (J = 1, K = 0) forces a set to 1. E merely pairs those set and reset conditions, so it is not toggle either.
Why this matters. The J = K = 1 state is the whole reason the J-K flip-flop was introduced: in an S-R flip-flop the equivalent input S = R = 1 is forbidden (indeterminate output), and the J-K's internal cross-coupled feedback turns that useless combination into a well-defined complement operation. Tying J and K permanently to 1 converts the device into a T (toggle) flip-flop, which divides the clock frequency by 2 and is the building block of ripple counters.
One practical caution. In a level-triggered (non-edge) J-K, holding J = K = 1 while the clock is high causes the output to oscillate repeatedly — the "race-around" problem — which is cured by edge-triggering or by the master–slave configuration.
Hence, the toggle condition occurs only for J = 1, K = 1, i.e. A only.
Similar Questions
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 ?
Which flip-flop can be used as latch ?
In a J-K FF, if J = Q and K = 1 (see figure). Assuming the flip flop was initially cleared and then clocked for 6 pulses, the sequence at the Q output will be :
Consider the following statements regarding registers and latches :
(A) Registers are made of edge triggered flip-flops whereas latches are made from level triggered flip flops
(B) Registers are temporary storage devices whereas latches are not
(C) A latch employs cross coupled feed back connections
(D) A register stores a binary word whereas a latch does notChoose the most appropriate answer from the options given below :
Match List I with List II
LIST I (Diagram) LIST II (Sequential Circuit) A. 
I. Edge triggered S-R flip flop B. 
II. D Flip flop to SR flip flop C. 
III. Gated Latch clocked flip flop D. 
IV. Gated D Latch Choose the correct answer from the options given below:
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 ?
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The basic sequential logic building block in which the output follows the data input as long as the ENABLE input is active, is
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