Solution:

New PCL-746+ rev. B1 has a great difference from the old version in jumper settings. New PCL-746+ has four independent I/O base address switches for each serial port, no matter in standard mode or enhanced mode. Position 1 of "interrupt reg. setting" switch is used to set mode, ON for standard mode, OFF for enhanced mode. When set to standard mode, the IRQ number of each port is set by JP1 to JP4 independently. JP4 for CH1, JP3 for CH2, JP2 for CH3 and JP1 for CH4. When set to enhanced mode, 4 ports share the same IRQ number set by JP4. JP1 to JP3 settings are ignored. Also user can read interrupt status from the I/O register set by nterrupt reg. setting?switch position 2-7. There are 4 jumpers to set RS-422 Rx always-ON mode. When JP25 to JP28 are shorted, the receiver will be always-ON. It suitable for RS-422 4-wire connection. When using RS-485 mode, these 4 jumpers must be opened. JP28 for CH1, JP27 for CH2, JP26 for CH3 and JP25 for CH4.