Solution:

When data arrives at one of four ports, it will generate an interrupt in the interrupt register. The PC software can read this and identify immediately which port generated the interrupt. This saves time and makes programming easier. When a data bit of the interrupt status register is set to 0, the corresponding channel is selected to generate an interrupt. If the bit is 1, then no interrupt is generated. However, this definition is reverse from Windows 95/98/NT. So JP15 for PCL-849 just designed for this purpose. Actually, Windows 95/98 don't provide SHARE IRQ feature, so the OS use POLLING method to achieve this goal. Only Windows NT SHARE IRQ feature. Besides, our PC-ComLIB, DOS Library, do use the vector address to achieve SHARE IRQ feature. However, PCL-746+ don't have the jumper for you to adapt OS, but PCL-846, PCL-847, PCL-849 and PCL-858 has. Mainly because PLC-746+ was developed early then PCL-846, PCL-847, PCL-849 and PCL-858, so, it don't need the VECTOR ADDRESS under Windows 95/98 and Windows NT. Under Windows system, the OS POLLING IRQ to achieve SHARE IRQ feature.