re soundblaster irq and port settings discussing the use of irq in recent article msprague superior mcwbst b mike sprague writes i as a number of poeple in this thread have already written i can t prove it s true but i believe it lpt does not actually use irq even though that interrupt is supposed to be dedicated to lpt to put it a little differently irq is the de facto standard interrupt assigned to be used by the printer adapter to announce its completion of some activity dos doesn t monitor irq it uses other means to determine when it s time to send out another byte to the printer most all hardware printer adapters have the ability to disable the use of irq usually by merely breaking the connection between the isa pin and the associated driver other adapters control the irq line by a tri state driver and by programming just leave it in the high impedence mode unfortunately there are a lot of adapter cards which use bistate drivers i e either assert high or assert low for the irq lines rather than tristate drivers assert high assert low or don t assert anything the presence of such a card on an irq line precludes the use of that irq by any other adapter unless it is physically disconnected by a jumper incidentally note that there s no requirement that a card hold the irq line low when no interrupt is desired if that were true you would have to somehow tie down all unconnected irq lines and that certainly isn t a requirement non dos operating systems os nt various unices or whatever the proper plural of unix might be require the use of irq for performance reasons and the sb alas is one of the cards which uses bistate drivers joe morris mitre jcmorris mitre org
