Encoders & Decoders MCQs

Practice Encoders & Decoders MCQs with four options, answers and explanations for focused Electronics & Telecommunication Engineering revision.

Question 1

Digital ElectronicsEncoders & Decoders

An encoder generally converts?

A2ⁿ input lines into n output lines
Bn input lines into 2ⁿ output lines
CAnalog voltage directly into frequency only
DSerial data into analog data

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Correct Answer: A. 2ⁿ input lines into n output lines

Explanation: A conventional binary encoder maps one active line among 2ⁿ inputs to an n-bit code.

Reference: Binary encoder fundamentals

Question 2

Digital ElectronicsEncoders & Decoders

A decoder generally converts an n-bit binary input into up to?

An output lines
Bn/2 output lines
C2ⁿ output lines
D2n input lines

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Correct Answer: C. 2ⁿ output lines

Explanation: A binary decoder can activate one of up to 2ⁿ output lines for an n-bit input.

Reference: Binary decoder fundamentals

Question 3

Digital ElectronicsEncoders & Decoders

A 3-to-8 decoder has an enable input and is enabled. For each valid 3-bit input, how many output lines are normally selected in a one-of-eight decoder?

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Correct Answer: A. 1

Explanation: A conventional 3-to-8 decoder activates one of eight outputs for each binary input combination.

Reference: Standard digital electronics: decoders

Question 4

Digital ElectronicsEncoders & Decoders

A priority encoder differs from an ordinary encoder because it?

AHas no outputs
BAssigns priority when more than one input is active
CAlways converts analog signals
DStores the encoded data permanently

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Correct Answer: B. Assigns priority when more than one input is active

Explanation: A priority encoder resolves simultaneous active inputs by producing the code corresponding to the highest-priority asserted input.

Reference: Standard digital electronics: priority encoders

Question 5

Digital ElectronicsEncoders & Decoders

How many 2-to-4 decoders with enable inputs are minimally needed to construct a 3-to-8 decoder using a straightforward hierarchical arrangement?

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Correct Answer: B. 2

Explanation: The most significant input can enable one of two 2-to-4 decoders, while the remaining two inputs feed both decoders. Thus two decoders are sufficient.

Reference: Standard digital electronics: decoder expansion

Question 6

Digital ElectronicsEncoders & Decoders

A priority encoder has a VALID output in addition to encoded outputs. The VALID signal is useful primarily to indicate that?

AAt least one encoder input is asserted
BAll inputs are necessarily asserted
CThe output code is analog
DThe clock has stopped

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Correct Answer: A. At least one encoder input is asserted

Explanation: Without a valid indication, the encoded output corresponding to no active input can be ambiguous with the code for a legitimate input. VALID indicates that an asserted input exists.

Reference: Standard digital electronics: priority encoder valid output

Question 7

Digital ElectronicsEncoders & Decoders

A decoder with active-LOW outputs is enabled. What does selection of one output normally mean?

AThe selected output goes LOW while the others remain HIGH
BThe selected output goes HIGH while all others go LOW
CAll outputs become high impedance
DEvery output toggles continuously

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Correct Answer: A. The selected output goes LOW while the others remain HIGH

Explanation: For an active-LOW decoder, assertion is represented by logic 0, so the selected output is LOW and unselected outputs remain HIGH.

Reference: Standard digital electronics: active-low decoders