8-Port, PCI, RS485/RS422 Serial Interface Device—The PCI‑8431/8 is a high-performance interface for high-speed communication with RS485 and RS422 devices. It features high-performance DMA transfers, multithreading, and multiprocessor support. You can also select between 4‑ and 2‑wire transceiver modes for full- and half-duplex communication. NI serial interfaces also appear as standard COM ports for compatibility with programs that use serial communications.