Solution:

Because PCL-749/840 is a communication card with jumpless setting, you need to use special utility instead of jumpers/switchs to set hardware configuration. This special utility is called "IO-IRQ.EXE" which is located in your utility disk. Before starting IO-IRQ.EXE, please make sure the original address setting for your card. If you forget the previous setting, please short JP1 and follow the hint to type in "A700", then the utility will show the default settings about I/O address and IRQ level for each COM port. The default settings for each port are listed: COM3 : I/O = 300 ~ 307Hex, IRQ = 10 COM4 : I/O = 308 ~ 30FHex, IRQ = 10 COM5 : I/O = 310 ~ 317Hex, IRQ = 10 COM6 : I/O = 318 ~ 31FHex, IRQ = 10 I/O Vector Address : 280 Hex Note!! Please run IO-IRQ.EXE under DOS environment