Solution:

Mainly because the PCL-746+ is our old product, and it was developed in the past few years, and the VECTOR ADDRESS designed is FAR FROM the standard of Windows 95/98/NT. In DOS and Windows 3.1 environment, when a data bit of interrupt status register is set to 0, the corresponding channel is select to generate an interrupt by using PC-COMLIB Utility. However, in Windows NT environment, when a data bit of interrupt status register is set to 1, the corresponding channel is select to generate an interrupt. BUT, the PCL-746+ can't change mode to adapt that. Besides, in Windows 95/98 environment, the operating system doesn't provide such function as VECTOR ADDRESS but SHARE IRQ. So you have to polling the address of VECTOR ADDRESS by your program.