The PCISA-7520 series card provides RS-232 to RS-485 (or RS-422) converter function that is exactly the same as I-7520 series. It is designed for easy installation, powered from the PCI or ISA Interface but without PCI and ISA functions. The PCISA-7520 series is equipped with both an RS-232 serial port and an RS-485 serial port. The RS-232 port is designed to communicate with the local Host PC, the RS-485 is designed to communicate with the remote IO module.
For adding more serial ports to a PC, please refer to VXC/VEX series cards.
http://www.icpdas.com/products/Industrial/multi_serial/multi_introductions.htm