re soundblaster irq and port settings in article pdb kilimanjaro jpl nasa gov pdb ipl jpl nasa gov paul bartholomew writes in article shaman wv tek com andrew frip wv tek com andrew klossner wrote these lpt com disk controller are call devices there are devices that requires exclusive interrupt ownership eg disk controller i and keyboard i there are also devices that does not require exclusive ownership ie it will share an interrupt with another device eg lpt 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 then it must hold a certain bus wire to or at all times depending on whether or not it wants an interrupt this precludes letting another card assert interrupt number 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 successfully i assure you that they are both set to irq and that i have no problem my computer is a dtk ibm clone simple first andrew is correct although i can see where there might be some confusion it is indeed possible to have two cards configured to use the same interrupt they can not share the interrupt in the sense that it is not possible to have both cards active at the same time here is an example for some time i was short of free interrupts i had a tape controller not a floppy tape that needed one of irq irq it s an old tape drive my solution was to use irq also used for com where my modem is i did this because i reasoned i would never be using the modem and the tape simultaneously when kermit runs it installs its own interrupt handler for irq and uses the serial port if the tape drive were to generate an interrupt kermit would not have a clue what to do with for the tape controller and since the tape controller would not be serviced it would most likely hang likewise when the tape backup software runs it installs an interrupt handler for irq that handler won t do anything for the serial port under dos printing is not interrupt driven instead the bios polls the status of the parallel port to determine when another byte may be sent that s why you can have your sound card and lpt both configured to use irq try that on nt and see how far you ll get kenneth r ballou voice oberon software inc fax one memorial drive cambridge ma internet ballou oberon com the views and opinions expressed above are my own and do not necessarily reflect those of my employer
