For the daisy chain scheme of connecting I/O devices, which of the following…
1996
For the daisy chain scheme of connecting I/O devices, which of the following statement is true?
- A.
It gives non-uniform priority to various devices
- B.
It gives uniform priority to all devices
- C.
It is only useful for connecting slow devices to a processor
- D.
It requires a separate interrupt pin on the processor for each device
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Show answer & explanation
Correct answer: A
In a Daisy Chain configuration, multiple I/O devices are connected to a single interrupt lines vector in a serial (linear) fashion.
How it works: When one or more devices pull the common interrupt request line, the processor responds by sending an Interrupt Acknowledge (INTA) signal. This signal enters the first device in the chain.
The Priority Rule: If the first device requested the interrupt, it intercepts the signal, places its vector address on the data bus, and does not pass the signal down the line. If it did not request an interrupt, it passes the INTA signal to the next device in the sequence.
The Outcome: Because the INTA signal travels sequentially from the physically closest device to the physically farthest device, the device closest to the processor has the absolute highest priority, while the device at the end of the chain has the lowest priority.
Therefore, the priority assigned to the devices is strictly non-uniform and depends entirely on their physical position in the chain.