Combinational Logic

Combinational Logic – Verified PYQ Authority Guide

Combinational Logic is organised as a topic-level PYQ authority page. It brings together the strongest verified question clusters, exam/year coverage and concept-level practice so students can revise the topic without jumping through unrelated notes. Every factual learning cue below is drawn from the existing verified, published and approved English PYQ corpus or from its Knowledge Graph relationships; the hub does not invent unsupported technical claims.

PYQ evidence snapshot

5 verified PYQs are currently mapped to this Topic hub. The represented years include 2026, 2025. Exam coverage currently includes Deputy Executive Engineer (Electrical), Class-2, Sports Authority of Gujarat / Assistant Engineer (Electrical), Class-2,, Assistant Engineer (Electrical), Class-2, Road and Building Department. Subject context includes Electrical Engineering. These values come from live mappings and can expand automatically when new verified PYQs are added.

Most useful verified PYQs to solve first

Start with the actual questions rather than memorising a generic note. The links below are ranked from the mapped corpus using repeat history and editorial quality, while the complete explanation stays on the individual question page.

1. Consider the following statements regarding Decoder circuit: 1. Decoder converts binary input into one-hot output activating only one output line. 2. It can be used for function generation and memory addressing operations.…
   Deputy Executive Engineer (Electrical), Class-2, Sports Authority of Gujarat / Assistant Engineer (Electrical), Class-2, · 2026 · One-Hot Decoding and Addressing
   A decoder maps an n-bit code to one of up to 2^n output lines, commonly as a one-hot output. Decoders are used in memory/address…
2. Consider the following statements regarding Digital Multiplexer: 1. A multiplexer selects one of many inputs based on select lines and routes it to a single output. 2. Number of select lines required…
   Deputy Executive Engineer (Electrical), Class-2, Sports Authority of Gujarat / Assistant Engineer (Electrical), Class-2, · 2026 · MUX Selection and Logic Implementation
   A multiplexer routes one of many data inputs to a single output according to select inputs. By wiring data inputs to constants/variables appropriately, a…
3. Consider the following statements regarding Combinational Logic: 1. Combinational circuits produce outputs based only on present input conditions without memory effect. 2. These circuits do not include feedback paths or storage elements…
   Deputy Executive Engineer (Electrical), Class-2, Sports Authority of Gujarat / Assistant Engineer (Electrical), Class-2, · 2026 · Memoryless Logic Circuits
   A useful classification test is whether the same present input can produce different outputs because of history. Adders, multiplexers, decoders and encoders are combinational;…
4. How many inputs are required for a 1-of-10 BCD decoder?
   Assistant Engineer (Electrical), Class-2, Road and Building Department · 2025 · BCD-to-Decimal Decoder Inputs
   A BCD digit represents decimal 0–9 using four binary bits (8421 code). Therefore a 1-of-10 BCD decoder needs 4 input lines and produces ten…
5. If A and B are the inputs of a half adder, then the sum is given by __________
   Assistant Engineer (Electrical), Class-2, Road and Building Department · 2025 · Half Adder Sum
   A half adder adds two single-bit inputs. Its Sum output is 1 only when A and B are different, which is exactly the XOR…

Formula & key-relationship bank from verified solutions

• n inputs → up to 2^n decoded outputs.
• N=2^m inputs for m select lines.
• Combinational: y(t)=f[x(t)]. Sequential: y(t)=f[x(t), state(t)], with state(t+1)=g[x(t),state(t)].
• BCD digit = 4 bits 2⁴ = 16 possible codes; 10 are valid decimal digits
• Sum S = A ⊕ B Carry C = A·B

Use these as revision triggers and open the linked PYQ before applying a formula numerically; variable definitions and assumptions belong to the exact solved question.

Core ideas repeatedly reinforced by the solved corpus

• A decoder maps an n-bit code to one of up to 2^n output lines, commonly as a one-hot output. Decoders are used in memory/address selection and can implement minterm-based logic functions. Key relation: n inputs → up to…
• A multiplexer routes one of many data inputs to a single output according to select inputs. By wiring data inputs to constants/variables appropriately, a multiplexer can implement Boolean functions. Key relation: N=2^m inputs for m select lines. Exam…
• A useful classification test is whether the same present input can produce different outputs because of history. Adders, multiplexers, decoders and encoders are combinational; counters, registers and finite-state machines are sequential. Key relation: Combinational: y(t)=f[x(t)]. Sequential: y(t)=f[x(t), state(t)],…
• A BCD digit represents decimal 0–9 using four binary bits (8421 code). Therefore a 1-of-10 BCD decoder needs 4 input lines and produces ten decoded output lines.
• A half adder adds two single-bit inputs. Its Sum output is 1 only when A and B are different, which is exactly the XOR truth table; the Carry output is A·B.

Exam tips already validated in SRO solutions

• Only the selected output is asserted in ideal one-hot decoding.
• MUX is both a selector and a logic-function building block.
• Ask one question: “Does previous state matter?” If no → combinational.
• Do not confuse number of outputs (10) with number of inputs (4).
• Memorize the pair together; exam distractors often swap Sum and Carry.

Common mistakes to avoid

• All decoder outputs are not active simultaneously.
• Do not claim a MUX cannot implement arbitrary Boolean functions.
• Treating “timing operation” as proof that a circuit is combinational.
• Answering 10 because it is a 1-of-10 decoder.
• Selecting OR for Sum; OR fails for A=B=1 because the correct sum bit is 0 with carry 1.

Topic and concept coverage

Mapped topic labels include Combinational Logic. The concept trail includes BCD-to-Decimal Decoder Inputs, Half Adder Sum, Memoryless Logic Circuits, MUX Selection and Logic Implementation, One-Hot Decoding and Addressing. Use these labels as a revision map: move from the broad area to the narrow concept, solve a verified PYQ, inspect the detailed reasoning, and then attempt another question from the same cluster.

Knowledge Graph navigation

Continue with Digital Electronics, Adders, Combinational versus Sequential, Decoders, Multiplexers, Electrical Engineering, BCD-to-Decimal Decoder Inputs, Half Adder Sum, Memoryless Logic Circuits. These are canonical SRO entity links based on the Knowledge Graph and shared question mappings, not keyword-stuffed tag pages.

How to revise this authority page efficiently

1. Solve before reading: answer a mapped PYQ first.
2. Read the exact explanation: verify the correct principle, formula, distractor logic and common mistake on that question page.
3. Move one level in the graph: use the closest concept/sub-topic/topic link rather than opening unrelated content.
4. Reattempt: solve another verified PYQ from this hub and check whether the same error repeats.

Quality scope: this page is automatically maintained from SRO’s verified mapped corpus. It enriches one canonical authority URL instead of generating multiple near-duplicate pages for keyword variants. Manual authority articles are never overwritten by the automated engine.