# Notes about interrupts

- Interrupt level 2 (IRQ 2/9)
  IRQ 2 does not conflict with any standard option boards but some manufacturers' communications adapters use this interrupt.
  IRQ 2 is sometimes referred to as IRQ 9. Interrupt levels 2 and 9 are equivalent.

- Interrupt level 3 (IRQ 3)
  IRQ 3 is the default interrupt. If your computer has a second serial port built in, or if it has an alternative asynchronous adapter, this uses IRQ 3. You may be able to disable the second serial port using your computer's configuration utility. If not, do not use IRQ 3 for your Smart 16/4 Fiber AT Ringnode.
  If you are installing more than one Ringnode in your computer, you can only use the default level (IRQ 3) for one of them. We recommend IRQ 12 or IRQ 15 as alternatives.
  IRQ 3 is also used by several types of IBM communications adapter and by the network adapters of some other manufacturers. If your computer already has one of the following IBM adapters installed, you cannot use IRQ 3 for your Ringnode:
  - SDLC (Synchronous Data Link Control) adapter
  - BSC (Binary Synchronous Communications) adapter

- Interrupt level 5 (IRQ 5)
  IRQ 5 is used by an alternative parallel port. If you have an alternative parallel port installed, and it is using interrupts, you cannot use IRQ 5 for your Ringnode.

- Interrupt level 7 (IRQ 7)
  IRQ 7 is used by the primary parallel port on your computer. If your parallel port is using interrupts, you cannot use IRQ 7 for your Ringnode.

- Interrupt levels 10, 11, 12 and 15 (IRQ 10, 11, 12, 15)
  Occasionally a device on your computer's motherboard may use one of these interrupts. For example, some Compaq computers use IRQ 12 for the mouse. If you suspect a problem for this reason, your computer's technical reference manual may help you decide which interrupt level to use.