From: pdb059@ipl.jpl.nasa.gov (Paul Bartholomew)
Subject: Re: Soundblaster IRQ and Port settings
Organization: Jet Propulsion Laboratory
Lines: 28
Distribution: world
NNTP-Posting-Host: kilimanjaro.jpl.nasa.gov

In article <3130@shaman.wv.tek.com>, andrew@frip.WV.TEK.COM (Andrew
Klossner) wrote:
> 
> []
> 
> 	"These LPT1, COM1, disk controller are call devices.  There are
> 	devices that requires exclusive interrupt ownership, eg. disk
> 	controller (I6) and keyboard (I1).  There are also devices that
> 	does not require exclusive ownership, ie. it will share an
> 	interrupt with another device, eg. LPT1"
> 
> No.  In a standard ISA bus, the one that almost all non-laptop PCs use,
> two separate interface cards cannot share an interrupt.  This is due to
> a screwup in the bus design.  For example, if your Soundblaster wants
> to drive interrupt number 7, then it must hold a certain bus wire to 0
> or 1 at all times, depending on whether or not it wants an interrupt.
> This precludes letting another card assert interrupt number 7.
> 
> When two or more devices in an ISA bus PC share an interrupt, it's
> because they're implemented by a single card.

Interesting.  Would you care to explain to me then, how my SoundBlaster
Pro card and my printer card are sharing IRQ 7 successfully?  I assure
you that they are both set to IRQ 7 and that I have no problem.  My
computer is a DTK 286-12 IBM clone.

Paul Bartholomew
pdb059@ipl.jpl.nasa.gov
