Which one of the following is true for a CPU having a single interrupt request…

Even with:

• One interrupt request line (IRQ)

• One interrupt grant line (INTA)

the system can still support:

Multiple interrupting devices

• Devices share the same interrupt request line

• Hardware (e.g., daisy chaining, priority encoders, or controllers) decides which device gets serviced

• Only one device responds when the CPU sends the interrupt grant

Vectored interrupts

• When the CPU asserts the interrupt grant line,
  the interrupting device places its interrupt vector number on the data bus

• CPU uses this vector to jump directly to the correct ISR

Hence, both vectored interrupts and multiple devices are possible

Option A

“Neither vectored interrupt nor multiple interrupting devices are possible.”

Why wrong:

• Multiple devices can share a single IRQ line

• Vectored interrupts do not require multiple IRQ lines

• Both are possible using arbitration and vector placement

Option B

“Vectored interrupts are not possible but multiple interrupting devices are possible.”

Why wrong:

• Vectored interrupts are possible even with a single IRQ

• The interrupting device can supply the vector via the data bus

Option D

“Vectored interrupt is possible but multiple interrupting devices are not possible.”

Why wrong:

• Multiple devices can share one IRQ line

• Priority mechanisms ensure only one device responds at a time