|The port address 02f8h is for COM2 (IRQ3). If you have it trying to use IRQ4 with that address, it won't work. Here are the COM Port "rules" for PCs:|
It is best to avoid trying to use COM3 and COM4, a lot of software/hardware really doesn't support it. But, if you "tell" a piece of software to use the modem at COM1, it will look at IRQ4/03F8h and if no modem responds (which it won't if it's set on address 02F8h) then the software won't "find" the modem. Your computer's mainboard also has built-in UARTs. If they are enabled and assigned the same address or IRQ as the UART on your modem, they will block software from finding the modem's UART. The 16550AF is a high speed UART and should be able to work up to 115200bps (or baud), typically a modem's UART speed will be set by the firmware's negotiation with another modem, the BAUD you set will be the MAX speed it will use.
The jumper switches on the back of the computer are unique to that make/model of computer. Don't mess with them until you find a manual/description of what each switch does. It's possible that some of them have something to do with IRQs, but they are just as likely to have something to do with processor type, memory, math coprocessor, etc.