PC WRmt: Interrupt Conflicts with LAN Card Installation

• Microsoft Mail Remote, Windows Client, version 3.2

SUMMARY

If you have a network interface card (NIC) installed on the system on which you run Microsoft Mail Remote version 3.2 for Windows, you should configure the NIC such that it does not use Interrupt Request (IRQ) 2, 3, or 4. Use IRQ 5 or higher to avoid problems with using the serial port or with its performance. (No matter which IRQ you use, verify that it does not conflict with another device.)

MORE INFORMATION

Personal computers commonly use hardware interrupt requests to support different peripheral equipment (or accessories). One of these peripherals, apart from your modem, can include a NIC to connect your computer to a local-area network (LAN).

Many common conflicts occur when two peripherals attempt to service the same IRQ. Some common uses of IRQ vectors are as follows:

   IRQ 2: forwards requests to IRQ 9 or higher
   IRQ 3: serial ports COM2 and COM4
   IRQ 4: serial ports COM1 and COM3
   IRQ 5: second parallel printer port (LPT2)
   IRQ 7: first parallel printer port (LPT1)

Additionally, the IRQ with a lower number has higher priority for service (in other words, IRQ 2 has priority over IRQ 3).

If your network card is installed and configured for IRQ 2, and your network is busy, serial communications on IRQ 3 or IRQ 4 can be impaired. If the IRQ 2 interrupt handler is busy for too long when a serial port interrupt occurs, the port will lose characters.

On an active network, if the network card is configured with a lower interrupt number than the serial interrupt, the port will lose a character occasionally. When this occurs, the packet that contains the character must be resent, and all packets in the modem buffers must be resent. This process can be time consuming, expensive, and can lead to unacceptably higher communication error rates.

If you can assign the network card to an IRQ that is not currently used on your PC, such as IRQ 5 (if you do not have a second parallel printer port installed), you can minimize data loss and its consequent retransmission caused by a busy network.