>Hi .. anybody can help me .. or give me some suggestion or idea?
>
>I have problem when using comm3 and comm4 for communication interface, to inform all of you that I used 4 (Four) comm port for communication interface, they are:
>
>COM1 -> Mouse
>COM2 -> Modem
>COM3 -> Read to machine
>COM4 -> Write to machine
>
>the problem are:
>
>1. When COM2 is running, COM3 does not works, unknowned characters received.
>2. When COM2 is not running, COM3 is working correctly, but COM4 does not work.
>3. Windows98 can not detect modem when I change the modem comm port to COM4 .. why?
>

The interrupts are shared between COM1 and COM3, and between COM2 and COM4 - if you must use them, one of each pair must be used with polled I/O and interrupts disabled. A number of vendors sell multiport boards (Digiboard is one) with drivers that handle these issues properly with their hardware - you need their hardware/software solution to avoid the issues.