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 Which one of the following is true for a CPU having a single interrupt request line and a single interrupt grant line?

  1. Neither vectored interrupt nor multiple interrupting devices are possible

  2. Vectored interrupts are not possible but multiple interrupting devices are  possible

  3. Vectored interrupts and multiple interrupting devices are both possible

  4. Vectored interrupts are possible but multiple interrupting devices are not possible

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Best answer
34 votes
34 votes

(C) is the correct answer. We can use one Interrupt line for all the devices connected and pass it through OR gate. On receiving by the CPU, it executes the corresponding ISR and after exec INTA is sent via one line. For Vectored Interrupts it is always possible if we implement in daisy chain mechanism.

Ref : Click Here 

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29 votes
29 votes

Answer is C.
Both Vectored interrupts and multiple interrupting devices are both possible.

You know about parallel & serial connection(Daisy Chain).
Multiple devices are connected serially.

This is how it looks like.

So how it handles multiple interrupts ?
By the way what does it mean by handling multiple interrupts?
It means handling the interrupt from multiple I/O devices, & when two or more devices cause interrupt simultaneously, we want to give priority to High priority I/O.

The way it is implemented is....
Even if one I/O device caused interrupt, we can know it...   but who raised it ?
Interrupt ACK is connected to I/O1  (I/O with Highest priority)
If the interrupt was caused by I/O1 then, it will not forward the signal to I/O2. So we can know it was caused by I/O1.
If it was caused by I/O3, then I/O1 will forward it, I/O2 wil forward it .. So it is caused by I/O3.
So we are checking from highest priority I/O to lowest priority.
If two or more device cause interrupt, then priority will be given to higher priority since ACK moves from highest priority, so it will not forward ACK, & we can know we have to serve it first.

13 votes
13 votes
C. is the right option.

Daisy chain can be used.
11 votes
11 votes

Vectored Interrupts are those interrupts in which an I/O module places it's word(usually it's address or a unique service identifier) on the bus so that the cpu can recognize the respective I/O module.

Using, single interrupt request line and single interrupt grant line, both multiple interrupts and vectored interrupts are possible.

Example : Intel 80386 configured with External Interrupt Arbiter : Intel 82C59A

The below read may be further useful

Source : William Stallings 9ed

So ans- (c)

Answer:

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