In a vectored interrupt
The branch address is assigned to a fixed location in memory
The interrupting source supplies the branch information to the processor
The branch address is obtained from a register in the processor
None of the above
ANSWER
The answer is (b): in a vectored interrupt the interrupting source supplies the branch information to the processor.
Official answer: BSource: ISRO's revised and final answer key of 16 February 2024
Interrupts are classified by how the processor finds the service routine. In a non-vectored interrupt, the service routine sits at a fixed address, or the processor polls the devices to find which one raised the request.
In a vectored interrupt, the interrupting device itself identifies its service routine. During the interrupt-acknowledge cycle, the device places a vector (an interrupt vector number or the branch address) on the data bus.
The processor uses this vector to branch to the service routine, usually through an interrupt vector table. No polling is needed, so the response is faster.
Option (a) describes a fixed-location scheme, which is the non-vectored case, so it is wrong.
Option (b) says the interrupting source supplies the branch information to the processor. This is the definition of a vectored interrupt, so it is correct.
Option (c) says the address comes from a processor register. In a vectored interrupt the device supplies the information, so (c) is wrong. Option (d) is wrong because (b) is correct.
KEY IDEA
In a vectored interrupt the device sends the vector, which tells the processor where its service routine is, so no polling is needed.
WATCH OUT FOR
Choosing (a) because a fixed address is involved. A fixed service-routine address belongs to a non-vectored scheme. In the vectored scheme the device chooses the vector, and the vector table maps it to the routine.
From the ISRO CS 2023 paper. Every question of this paper · The full paper (PDF, ISRO) · All 2 ISRO I/O, interrupts & DMA questions, with notes
