TCS - More Golden Rules of Modems
More Golden Rules of Modems
by Bruce Carson
Tulsa Computer Society
From the December 1996 issue of the I/O Port Newsletter
If you have a computer with a sound card
and later decide to install an internal modem,
this article is for you.
There are precious few interrupt requests (IRQ's) available in our computers (16 total). Meanwhile as computer technology expands, more and more devices need those interrupts. Sound cards are greedy by design. Where most devices need only one interrupt, sound cards want two. Fortunately sound cards are very flexible as to which two IRQ's they will use, however modems are not. Typically internal modems work well on Com 3 Interrupt 5. If however your sound card was installed first, it will grab IRQ 5 which is normally for a second parallel printer (but not really needed in most cases.) This will cause a problem for the modem which can normally use only IRQ 3, 4, or 5. If the Modem is installed first and set for IRQ 5 then when the sound card is installed later, it will see that IRQ 5 is already in use, and will choose another.
If you already have a sound card installed, and wish to install an internal modem, the easiest way out of this problem is to change your mind and install an external modem instead. If you have a compelling requirement for an internal modem then the way to cure the problem is to physically remove the sound card and all its drivers. Then install and configure the internal modem. Last, reinstall and reconfigure the sound card. I know this sounds like a lot of trouble, but in comparison to the aggravation that can be caused by interrupt conflicts this is by far the lesser of the two evils. In any case, good luck.
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Tulsa Computer Society 02/18/97
Don Singleton, President
tcs@galstar.com