Interpreting K-map entries — meaning of a '1' in a cell. In a Karnaugh map used for SOP minimization, each '1' placed in a square represents what condition?
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Aa HIGH for each input truth table condition that produces a HIGH output.
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Ba HIGH output on the truth table for all LOW input combinations.
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Ca LOW output for all possible HIGH input conditions.
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Da DON'T CARE condition for all possible input truth table combinations.
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Ea hazard-free region independent of input changes.
Answer
Correct Answer: a HIGH for each input truth table condition that produces a HIGH output.
Explanation
Introduction / Context:Karnaugh maps are populated with 1s, 0s, and sometimes Xs (don’t care) to represent the output of a Boolean function for every input combination. Understanding exactly what a '1' means is essential for forming correct groups when obtaining a minimized sum-of-products expression.
Given Data / Assumptions:
- K-map arranged with Gray-coded rows/columns.
- We are targeting an SOP (sum-of-products) simplification.
- Entries may be 1 (true), 0 (false), or X (don’t care).
Concept / Approach:For SOP, we group adjacent 1s (including wrap-around) in sizes of 2^k to form product terms that evaluate to 1 for those input combinations. Each 1 corresponds to a minterm in the truth table where the function’s output is HIGH.
Step-by-Step Solution:
Identify all cells with 1s (true minterms).Create the largest possible adjacent groups of 1s (1, 2, 4, 8, …).Translate each group into a simplified product term by dropping varying literals.Sum the terms to form the minimized SOP expression.Verification / Alternative check:Reconstruct the truth table from the minimized SOP and verify that it yields 1 for exactly the minterms marked by 1s in the K-map and 0 elsewhere (except Xs which are don’t care conditions).
Why Other Options Are Wrong:
- All LOW input combinations: not specific; only certain input combinations produce 1s.
- LOW for all HIGH inputs: contradicts SOP mapping.
- DON’T CARE for all inputs: Xs are don’t care; 1s are definite HIGHs.
- Hazard-free region: hazards are timing-related; a 1 cell does not guarantee hazard-free behavior.
Common Pitfalls:
- Treating Xs as mandatory 1s; Xs are optional and used for larger groupings.
- Forgetting wrap-around adjacency on map edges.
Final Answer:a HIGH for each input truth table condition that produces a HIGH output.