 # Digital Electronics Question and Answer

Q.Define combinational logic

When logic gates are connected together to produce a specified output for certain
specified combinations of input variables, with no storage involved, the resulting circuit is called combinational logic.

The logic circuit that performs the addition of two bits is a half adder. The circuit that

Q. Define Decoder

A decoder is a multiple - input multiple output logic circuit that converts coded inputs into coded outputs where the input and output codes are different.

Q. What is binary decoder?

A decoder is a combinational circuit that converts binary information from n input
lines to a maximum of 2 n out puts lines.

Q. Define Encoder?

An encoder has 2 n input lines and n output lines. In encoder the output lines generate
the binary code corresponding to the input value.

Q. What is priority Encoder?

A priority encoder is an encoder circuit that includes the priority function. In priority
encoder, if 2 or more inputs are equal to 1 at the same time, the input having the highest priority will take precedence.

Q. Define multiplexer

Multiplexer is a digital switch. If allows digital information from several sources to be
routed onto a single output line.

Q. What do you mean by comparator

A comparator is a special combinational circuit designed primarily to compare the
relative magnitude of two binary numbers.

Q. What are the classification of sequential circuits?

The sequential circuits are classified on the basis of timing of their signals into two
types.

They are,

1)Synchronous sequential circuit.
2)Asynchronous sequential circuit.

Q. Define Flip flop.

The basic unit for storage is flip flop. A flip-flop maintains its output state either at 1
or 0 until directed by an input signal to change its state.

Q.What are the different types of flip-flop?

There are various types of flip flops. Some of them are mentioned below they are,

• RS flip-flop
• SR flip-flop
• D flip-flop
• JK flip-flop
• T flip-flop

Q.What is the operation of D flip-flop?

In D flip-flop during the occurrence of clock pulse if D=1, the output Q is set and if D=0, the output is reset.

Q. What is the operation of JK flip-flop?

• When K input is low and J input is high the Q output of flip-flop is set.
• When K input is high and J input is low the Q output of flip-flop is reset.
• When both the inputs K and J are low the output does not change
• When both the inputs K and J are high it is possible to set or reset the flip-flop (ie) the output toggle on the next positive clock edge.

Q. What is the operation of T flip-flop?

T flip-flop is also known as Toggle flip-flop.

• When T=0 there is no change in the output.
• When T=1 the output switch to the complement state (ie) the output
toggles.

Q. Define race around condition.

In JK flip-flop output is fed back to the input. Therefore change in the output results
change in the input.

Due to this in the positive half of the clock pulse if both J and K are high then output toggles continuously. This condition is called ‘race around condition’.

Q. What is edge-triggered flip-flop?

The problem of race around condition can solved by edge triggering flip flop. The
term edge triggering means that the flip-flop changes state either at the positive edge or negative edge of the clock pulse and it is sensitive to its inputs only at this transition of the clock.

Q. What is a master-slave flip-flop?

A master-slave flip-flop consists of two flip-flops where one circuit serves as a master and the other as a slave.

Q .Define registers.

A register is a group of flip-flops flip-flop can store one bit information. So an n-bit register
has a group of n flip-flops and is capable of storing any binary information/number
containing n-bits.

Q.Define shift registers.

The binary information in a register can be moved from stage to stage within the
register or into or out of the register upon application of clock pulses. This type of bit movement or shifting is essential for certain arithmetic and logic operations used in microprocessors. This gives rise to group of registers called shift registers.

Q.What are the different types of shift type?

There are five types. They are,

• Serial In Serial Out Shift Register
• Serial In Parallel Out Shift Register
• Parallel In Serial Out Shift Register
• Parallel In Parallel Out Shift Register
• Bidirectional Shift Register

Q.Define synchronous sequential circuit

In synchronous sequential circuits, signals can affect the memory elements only at discrete instant of time.

Q. Define Asynchronous sequential circuit?

In asynchronous sequential circuits change in input signals can affect memory element at any instant of time.

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