Question on IRQ's

[Bill in SD, CA]

IRQ's go from 0 -15. Is their numbering therefore related to hexadecimal?

Thanks,

Bill

[dunbar]

yes, cascading a second group of 8 onto one of the first 8 addresses.

HTH.

[Beemer]

Your devices/components have a baseaddress which is a hexadecimal and the IRQ is related to by decimal. You could convert a decimal to a hexadecimal I guess. Is there a reason for this query?

Cheers!

[Bill in SD, CA]

Studying for A+ and I just looked at the 0 thru 15 assignments and noticed the relationship to the hex system. Just wanted confirmation that my observation was correct.

Thanks! Back to the books.

Bill

[John Prophet]

hmmm, I dont remember IRQs having anything to do with hex.

Evidently the first comps had maybe 8 IRQ's cuz they used one chip with 8 bits...then they needed more IRQs so they added another chip but to make it all backwardly compatible they connected one of the "wires" of the first chip to the other chip so theyre are only 15 IRQ's since the two that are connected are obviously then just become one. 8+7=15

I believe it is IRQ 2 that is then connected to IRQ 9..so in reality there is no IRQ 2 since it has become IRQ 9. These are the two that are connected.

Here is one article, there are many on the internet http://www.pcguide.com/ref/mbsys/res/irq/num.htm

I know you are studying for A+. They are not gonna get into super great detail about this. Mainly I would remember the IRQ numbers and I/O addresses of the parallel ports and the COM ports and maybe remember some of the typical standard IRQs.

For example 1 is always gonna be keyboard
6 is gonna ne floppy controller.

etc.

The hex stuff comes in on the I/O addresses..again the thing id remember there would be the I/O addresses (and IRQs) of the LPT (parallel) ports and the COM (serial) ports.

JP

[John Prophet]

As far as any relationship of IRQ to the hex addresses etc...I dont see it.

For example we can force a certain pci card to take another IRQ but it doesnt have to also change the hex I/O address.

JP

[Bill in SD, CA]

Thanks for the info. I see your point. Now it looks like maybe a coincidence. Just trying to understand.

That's why TechIMO is my fallback when I get confused.

Bill

[dr_roberts49]

What would interest me on IRQs, is to easily assign ONE IRQ to my soundcard, and ONE to my video card. All the rest can share. I've found no simple way of doing this, without changing slots, and playing roulette in the bios. Royal pain in the butt.

Robert

[Peter M]

Nothing in computers is hex or dec. It's all binary.

The 15 system IRQs are because the Intel 8259 interrupt controller first used in the original PC had eight inputs. When the AT was built, another one was added, cascading its output onto one input of the one that was already there. 8+8-1 = 15. That was in 1983, and that's what we still have - unless the system uses the more recent APIC interrupt controllers.

[Peter M]

Besides, there is no relation between resources. Memory, I/O, and IRQ allocations in PCI devices are all independent and arbitrary.
Likewise, IRQ sharing is a specific, mandatory design feature that everything PCI and AGP is required to comply to. There is no need to do what you want to do. Shared IRQs being a problem is a myth that roots back in the ISA days.