COM ports/IRQs Help

bobbyb33bobbyb33 Junior MemberMember Posts: 4 ■□□□□□□□□□
Can anyone help me to understand COM/IRQ i'm readinng the AIO book
and don't get this part. it seems like the book's saying two devies can't share an IRQ then it mentions later that devices can share. i can't get my head round COM/IRQ can anyone help? icon_confused.gif:


  • IMuaTechIMuaTech Junior Member Member Posts: 12 ■□□□□□□□□□
    got this from
    It is possible to share an IRQ among more than one device, but only under limited conditions. In essence, if you have two devices that you seldom use, and that you never use simultaneously, you may be able to have them share an IRQ. However, this is not the preferred method since it is much more prone to problems than just giving each device its own interrupt line.

    One of the most common problems regarding shared IRQs is the use of the third and fourth serial (COM) ports, COM3 and COM4. By default, COM3 uses the same interrupt as COM1 (IRQ4), and COM4 uses the same interrupt as COM2 (IRQ3). If you have a mouse on COM1 and set up your modem as COM3--a very common setup--guess what happens the first time you try to go online? :^) You can share COM ports on the same interrupt, but you have to be very careful not to use both devices at once; in general this arrangement is not preferred.
  • WebmasterWebmaster Johan Hiemstra Admin Posts: 10,292 Admin
    The AIO is probably referring to IRQ steering / IRQ sharing. Try a search in our forums or google.

    Here's an example:;EN-US;314068
  • bobbyb33bobbyb33 Junior Member Member Posts: 4 ■□□□□□□□□□
    thank you that helps alot cheers
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