National Instruments 781473-01 Serial Interface Module 

National Instruments part number 781473-01 is an identifying part number for the PXIe-8431/8, a PXI Serial Interface Module with 8 ports and RS-422 and RS-485 Supported Serial Protocols. This NI Serial Interface Module stands out as a high-performance interface designed for swift communication with RS485 and RS422 devices. Equipped with high-performance DMA transfers, multithreading, and multiprocessor support, it ensures efficient data handling. This module allows users to have the flexibility to choose between 4‑ and 2‑wire transceiver modes, catering to both full- and half-duplex communication needs. 

Moreover, NI serial interfaces such as the 781473-01emulate standard COM ports, ensuring seamless compatibility with programs utilizing serial communications. In this setup, one device is designated as the Master while others operate as Slaves, enabling communication solely between the Master and the Slaves. No data exchange occurs among the Slaves themselves. Typically, the RS-422 controller functions as the master, with RS-485 devices serving as slaves, primarily for system optimization purposes. Initially, RS-422 infrastructure involves the utilization of 4-wire shielded twisted pair cables but facilitates connections solely between one device to another (up to 5 controllers and up to 10 receivers per controller). 

The NI 781473-01 incorporates the Modbus communication protocol, adhering to a client-server architecture. Commonly employed in IT, Modbus facilitates connectivity between electrical devices. This model features a transmission mode that delineates the structure of various data blocks within messages, crucial for data transmission. Within the Modbus framework, there exist two transmission modes, both ensuring seamless compatibility when interfacing with slaves.