7485 magnitude comparator outputs for A = 1001 and B = 1010 For a 7485-style 4-bit magnitude comparator, determine the outputs A<B, A=B, and A>B when inputs are A = 1001 (decimal 9) and B = 1010 (decimal 10).
Digital Electronics
MSI Logic Circuits
Difficulty: Easy
Choose an option
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AA < B is 1 A = B is 0 A > B is 1
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BA < B is 0 A = B is 1 A > B is 0
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CA < B is 0 A = B is 0 A > B is 1
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DA < B is 1 A = B is 0 A > B is 0
Answer
Correct Answer: A < B is 1 A = B is 0 A > B is 0
Explanation
Introduction / Context:Magnitude comparators output three mutually exclusive flags indicating less-than, equal, or greater-than relationships between binary words. Practicing with specific inputs develops fluency useful for timing and control logic.
Given Data / Assumptions:
- A = 1001 (binary) = 9 (decimal).
- B = 1010 (binary) = 10 (decimal).
- No cascading inputs are asserted; we consider only local comparison.
Concept / Approach:Compare bit by bit from MSB to LSB. The first position where A and B differ determines the outcome. Alternatively convert to decimal and compare numerically.
Step-by-Step Solution:
A = 1001, B = 1010 → MSB bits are 1 for both; continue.Next bits: 0 (A) vs 0 (B) → equal; continue.Next: 0 (A) vs 1 (B) → A < B at this position; we can conclude A < B overall.Therefore outputs: AB = 0.Verification / Alternative check:Decimal comparison: 9 < 10, so A
Why Other Options Are Wrong:
- Equal or A>B asserted: These contradict the bitwise or decimal comparison.
- Multiple flags true: In a proper comparator only one of AB can be 1 at a time.
Common Pitfalls:
- Comparing from LSB upward; significant bits must be examined first because they carry higher weight.
Final Answer:A < B is 1, A = B is 0, A > B is 0.