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?

I can not change the IRQ setting for COM3 & COM4.., the COM1's IRQ is same as COM3's IRQ and also COM2's IRQ is same as COM4's IRQ

I don't know why .. it's seems like the COM3 / COM4 I/O does not received enough power to do some process.