Parity systems: “In a parity generator circuit, an error is signaled on an error indicator.” This statement is ________.
-
AIncorrect
-
BCorrect
-
CCorrect only for even parity
-
DCorrect only with 9-bit UART frames
-
ECorrect when combined with CRC
Answer
Correct Answer: Incorrect
Explanation
Introduction / Context:Parity subsystems often include both generation and checking functions, sometimes within the same integrated circuit. However, the roles are distinct: the generator creates a parity bit from data; the checker compares received data and parity to detect errors. This question probes whether you can distinguish those responsibilities.
Given Data / Assumptions:
- Parity generator: Computes parity bit from local data (transmit side).
- Parity checker: Examines incoming data plus parity to detect mismatches.
- Some ICs combine both functions, but the logic blocks remain conceptually separate.
Concept / Approach:Only the checker asserts an error indicator because it performs a comparison between expected parity (recomputed from received data) and the received parity bit. A pure generator does not perform comparison and therefore has no basis to assert an error flag. Confusion arises because catalog parts may be titled “parity generator/checker.”
Step-by-Step Solution:
On transmit: generator computes p so data+p has the required parity.On receive: checker recomputes parity p′ from data and compares against received p.If p′ ≠ p, checker raises an error indicator.Therefore, a generator alone has nothing to compare and cannot signal an error.Verification / Alternative check:Examine block diagrams of common parts (e.g., parity generator/checker devices): separate logic blocks are shown for generation and checking, with the error output present on the checker side only.
Why Other Options Are Wrong:
- Correct/only for even parity/with specific frames/with CRC: All imply a generator signals errors, which it does not. CRC is unrelated to a simple parity generator’s function.
Common Pitfalls:Assuming “generator” and “checker” are interchangeable; overlooking that error detection requires comparison between expected and actual parity, which a generator does not perform.
Final Answer:Incorrect