# Digital Circuits Questions and Answers – Flip Flops

This set of Digital Electronics/Circuits Multiple Choice Questions & Answers (MCQs) focuses on “Flip Flops

1. The basic latch consists of ___________
a) Two inverters
b) Two comparators
c) Two amplifiers

Explanation: Two inverters make up the basic latch. It means that if the first output Q = 0, the second output Q’ must be 1, and vice versa.
2. In S-R flip-flop, if Q = 0 the output is said to be ___________
a) Set
b) Reset
c) Previous state
d) Current state

Explanation: In S-R flip-flop, if Q = 0 the output is said to be reset and set for Q = 1.
3. The output of latches will remain in set/reset untill ___________
a) The trigger pulse is given to change the state
b) Any pulse given to go into previous state
c) They don’t get any pulse more
d) The pulse is edge-triggered

Explanation: Until the trigger pulse is delivered to change the state, the latches’ output will stay set/reset.
4. What is a trigger pulse?
a) A pulse that starts a cycle of operation
b) A pulse that reverses the cycle of operation
c) A pulse that prevents a cycle of operation
d) A pulse that enhances a cycle of operation

Explanation: Trigger pulse is defined as a pulse that starts a cycle of operation.
5. The circuits of NOR based S-R latch classified as asynchronous sequential circuits, why?
a) Because of inverted outputs
b) Because of triggering functionality
c) Because of cross-coupled connection
d) Because of inverted outputs & triggering functionality

Explanation: A feedback path is formed by cross-coupled connections from one gate’s output to the input of another gate. As a result, NOR-based S-R latch circuits are classed as asynchronous sequential circuits. Furthermore, they are referred to as asynchronous since they do not require a clock pulse to operate.

6. Latches constructed with NOR and NAND gates tend to remain in the latched condition due to which configuration feature?
a) Low input voltages
b) Synchronous operation
c) Gate impedance
d) Cross coupling

Explanation: The latch is a bistable multivibrator with two stable states. A latch’s two inputs are connected directly to each other’s output. Cross coupling is a sort of construction that allows latches to remain in the latched position.

7. One example of the use of an S-R flip-flop is as ___________
a) Transition pulse generator
b) Racer
c) Switch debouncer
d) Astable oscillator

Explanation: The SR flip-flop is especially good at reducing the effects of switch bounce, which is the unpleasant noise that occurs when electronic equipment are switched on and off.

8. The truth table for an S-R flip-flop has how many VALID entries?
a) 1
b) 2
c) 3
d) 4

Explanation: Set, Reset, and the current state are the three inputs to the SR flip-flop. When S and R are both at 1, the Invalid or Undefined State occurs.

9. When both inputs of a J-K flip-flop cycle, the output will ___________
a) Be invalid
b) Change
c) Not change
d) Toggle

Explanation: After one cycle, the values of all the inputs are the same. For example, assume J=0 and K=1. J=0->1->0 (after one cycle) and K=1->0->1 (after one cycle) (1 cycle complete). Latch, Reset, Set, and Toggle are the four stable states of the J & K flip-flop.
10. Which of the following is correct for a gated D-type flip-flop?
a) The Q output is either SET or RESET as soon as the D input goes HIGH or LOW
b) The output complement follows the input when enabled
c) Only one of the inputs can be HIGH at a time
d) The output toggles if one of the inputs is held HIGH

Explanation: When the clock is high in a D flip flop, the output is determined by the input; otherwise, the previous output is remembered. When the clock is high, the output Q is also high; if the clock is low, the output is zero. The D-flip-flop, like the SR flip-flop, has an incorrect state at both inputs of 1.
11. A basic S-R flip-flop can be constructed by cross-coupling of which basic logic gates?
a) AND or OR gates
b) XOR or XNOR gates
c) NOR or NAND gates
d) AND or NOR gates

Explanation: Cross coupling of NOR or NAND gates can be used to make the basic S-R flip-flop. Cross coupling occurs when the output of the second gate is fed into the first gate’s input and vice versa.
12. The logic circuits whose outputs at any instant of time depends only on the present input but also on the past outputs are called ________________
a) Combinational circuits
b) Sequential circuits
c) Latches
d) Flip-flops

Explanation: The output signals of sequential circuits are transmitted back to the input side. Sequential circuits are those whose outputs at any given time are determined not only by the current input but also by previous outputs. Combinational circuits, unlike sequential circuits, have output that is solely dependent on the current state.
13. Whose operations are more faster among the following?
a) Combinational circuits
b) Sequential circuits
c) Latches
d) Flip-flops

Explanation: Sequential circuits are often slower than combinational circuits. Because sequential circuits require memory devices to conduct their operations in order, combinational circuits do not require memory elements. Sequential circuits include latches and flip-flops.

14. How many types of sequential circuits are?
a) 2
b) 3
c) 4
d) 5

Explanation: Sequential circuits are divided into two types: synchronous or clocked circuits and asynchronous or unclocked circuits. Synchronous Sequential Circuits are activated by a clock signal, whereas Asynchronous Sequential Circuits are not triggered by a clock signal.
15. The sequential circuit is also called ___________
a) Flip-flop
b) Latch
c) Strobe