Which of the following is correct statement ?
2017
Which of the following is correct statement ?
- A.
In memory - mapped I/O, the CPU can manipulate I/O data residing in interface registers that are not used to manipulate memory words.
- B.
The isolated I/O method isolates memory and I/O addresses so that memory address range is not affected by interface address assignment.
- C.
In asynchronous serial transfer of data the two units share a common clock.
- D.
In synchronous serial transmission of data the two units have different clocks.
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Correct answer: B
Correct statement: The isolated I/O method isolates memory and I/O addresses so that memory address range is not affected by interface address assignment.
Why this is correct: Isolated I/O (port-mapped I/O) provides a separate I/O address space. Devices use port addresses and are accessed with special I/O instructions (e.g., IN/OUT), so device addresses do not occupy the memory address range.
Why the memory-mapped I/O statement is wrong: In memory-mapped I/O, device registers are mapped into the processor's memory space and are accessed with normal memory instructions, so they do occupy memory addresses.
Why the asynchronous serial statement is wrong: Asynchronous serial communication does not use a shared continuous clock. Instead both ends agree on a baud rate and use start/stop bits (and optionally parity) to frame characters, allowing each end to recover timing locally.
Why the synchronous serial statement is wrong: Synchronous serial transmission requires clock synchronization; the units share timing either via a separate clock line or by embedding clock information in the data stream, so they do not operate with independent clocks.