Microsoft Windows 95 - Brainboxes RS422 Manual

AT & OPTO DUAL RS422/485

Microsoft Windows 95.

The Windows 95 environment now supports up to 255
standard serial ports, RS232, RS422 and RS485 etc.
If more than 2 serial ports are installed then the default
assignments assumed by Windows 95 will most probably need to be
changed. Windows 95 assumes that COM1 is on IRQ4 and that
COM2 is on IRQ3. For ports above COM2, Windows 95 makes an
attempt to detect the interrupt line being used. It is not always
successful. Obviously having more than just a couple of standard
serial ports in your PC will lead to Interrupt Request Line resource
conflicts, Windows 95 has gotten around this problem by letting
multiple ports be defined as sharing the same interrupt. Since the
PC bus does not allow interrupt sharing, any ports defined as
sharing interrupts cannot be used simultaneously, and even using
them individually slows down performance, as Windows 95 must
search through all defined ports using that interrupt to determine
which one has valid data arriving. Although an improvement on
Windows 3.x, the solution is still not ideal.
To obtain trouble free mix and match of the COM ports,
assuming that only 1 Serial Port already exists on your PC,
Set COM2, and COM3 interrupts to ones not used by other
devices in your system, say IRQ3, and IRQ10 respectively. Plug in
the card.
Click the Start button and select Settings, then Control Panel.
*
Software Configuration
Chapter 4 Page 39