The most ideal solution for the serial emulator card is for broad compatibility in systems, and ease of setup. Since IRQ 12 is normally associated with PS/2 mice, I thought IRQ 12 would be a nice fit. If your computer doesn't have a PS/2 mouse, IRQ 12 is usually available. IRQ 5 is often used by audio cards. IRQ 7 is used by LPT, but rarely used these days. IRQ 2/9 is also a nice idea, but some motherboards like to assign IRQ 2/9 to VGA. For future PCB/firmware revisions, the option for IRQ 2 could benefit some, as well as IRQ 12 and maybe IRQ 7. If you make a longer 16-bit ISA card, it can still go into 8-bit slots, but won't be able to use IRQ 12.
I think there will be a good number of WinBIOS users who want the serial emulator card, because in my experience, very few WinBIOS motherboards have PS/2 mouse support.
RIO444 wrote: "when 3E8 is assigned to Serial port1), try to remove the disconnected COM1 port in Windows and search for hardware using "Add New Hardware" in the Control Panel. "
I did remove the 'disabled COM1 (3E8)' from device manager, then I rebooted. Windows finds a new "Communications Port", but did not assign a COM# to it. When I reboot the system, the computer freezes shortly after the desktop appears. I rebooted again, and the computer froze again shortly after the desktop appears. Perhaps a problem due to IRQ 4 sharing? I booted into Safe Mode and opened the Device Manager, I see COM2 and COM3 listed, but COM1 is not listed.
Is it typical that two COM ports can share an IRQ and both be functional and different times? What about simultaneously? From the above test results, my NexGen system does not allow two COM ports to have the same IRQ (freezes). If you were to add some features to the adapter, I think IRQ's 2, 12, and maybe 7 could benefit some people, but only if standard mouse drivers work. If you add these extra IRQ's, COM 3/4 (and maybe COM 5?) should be added.
For others who obtain this emulator card, if you run into my issue and can't boot the system, I recommend connecting a standard serial port to COM2. Then boot Windows and disable COM1 in the device manager. Then put the RIO444's serial emulator card back in.
Even if you do not add additional IRQ support, I am very satisfied with the emulator card. It works fantastic and there is no noticeable lag when using my KVM, even with a trackball mouse. All other serial-to-PS/2 protocol converters I've tried, which is about 6 different devices, have all had mouse pointer lag issues when used through a KVM.