re soundblaster irq and port settings pdb ipl jpl nasa gov paul bartholomew writes clip clip 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 running ms dos or a derivative os obviously please take note that the following is not what exactly happens but a slightly simplified explanation technically the irq line is only a means for the device printer adapter soundblaster modem hard disk to signal the cpu that something s happening here please take note how the cpu is programmed to handle this signal is usually up to the operating system in ms dos the interrupt vector is used to store the address of the function that handles each interrupt now basic dos doesn t care whether the printer reports that it s ready to print some more stuff or not it simply ignores the interrupt when dos prints it looks at the lpt buffer if there s a character there wait a while and check again if there s not copy a new character to the lpt port since the irq is ignored as a printer interrupt it s free for use for any other adapters in this case the sb with any multitasking or otherwise advanced os this kind of printing approach just doesn t work or more precisely it wastes a lot of cpu cycles hence you can t share the irq with lpt and sb if you re running unix or os or whatnot another issue with the sb is that only the digitized sound uses interrupts when the sb plays plain music the cpu simply tells it what to play until told otherwise with digitized sound the interrupt is required to notify the cpu when the output ends and new data is needed you can however hook two or more com ports to one interrupt but use them only one at a time this is because the interrupt handling routine is same for both ports and it can see from which port the data came from this of course applies for some other devices like lpt as well remember this was greatly simplified in parts but i think gives the general picture correctly enough cheers juha liukkonen aka jliukkon cc helsinki fi university of helsinki dept of lost souls trust me i know what i m doing sledge hammer
