BCD validity check — Determine the decimal status of the single BCD nibble 1010. Is it a valid decimal digit encoding?
Electronics
Number Systems and Codes
Difficulty: Easy
Choose an option
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A8
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B10
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C12
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Dinvalid
Answer
Correct Answer: invalid
Explanation
Introduction / Context: Standard BCD uses a 4-bit group to encode decimal digits 0 through 9. Codes from 1010 to 1111 are not valid for a single BCD digit and are typically flagged as errors or treated as undefined in hardware decoders. This question tests recognition of invalid BCD patterns.Given Data / Assumptions:
- Single BCD nibble presented: 1010.
- Valid BCD set is 0000–1001.
- We are not using special variants like zoned or signed BCD here.
Concept / Approach: Because BCD mirrors decimal digits, any 4-bit value above 1001 does not represent a valid decimal digit. The pattern 1010 equals decimal 10 in pure binary, but BCD cannot encode decimal 10 as a single digit; two digits are required (1 and 0).Step-by-Step Solution:
List valid patterns: 0000–1001 only.Compare 1010 against the valid range.Conclude that 1010 is outside the valid BCD digit set.Verification / Alternative check:
Check a 7-segment decoder truth table; inputs above 1001 are undefined or treated specially.Why Other Options Are Wrong:
8, 10, 12: These are decimal interpretations of binary values, not BCD-valid single digits; 10 and 12 require two decimal digits.Common Pitfalls:
Confusing pure binary value with BCD digit validity.Assuming any 4-bit pattern is an acceptable BCD digit, which is not the case.Final Answer:
invalid