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National Instruments 779948-01 PXI Serial Interface Module 

National Instruments part number 779948-01 is an identifying part number for the PXI-8430/16 a PXI Serial Interface Module with 16 ports. The NI 779948-01, supports high-performance DMA transfers, multithreading, and multiprocessor capabilities. Unlike traditional interrupt-based serial interfaces, it enables simultaneous high-speed communication across multiple ports within a single system with minimal CPU usage. The NI-VISA API simplifies serial programming in NI LabVIEW and other languages, ensuring code compatibility across all VISA-compatible interfaces. 

It appears as standard COM ports, facilitating compatibility with software that uses serial communications. For high-speed digitizers, built-in memory typically handles sample storage, but situations may arise where data exceeds available memory. In such cases, understanding how digitizers use DMA to transfer data between the card and PC via the PCI interface is crucial. Initiating a "Fetch" operation starts the data transfer process, moving acquired signal samples from the digitizer's memory to the PC efficiently using DMA technology. RS-232 communication features single-ended transmission lines, supporting a maximum of one driver and one receiver. The maximum cable length is equivalent to 2.5 nanofarads (nF), ensuring efficient signal transmission over short to moderate distances. 

RS-232 interfaces such as the 779948-01 can withstand a Common Mode Voltage (CMV) of up to ±25 volts, providing robust protection against electrical noise and voltage fluctuations. Driver outputs range from 5 to 25 volts, delivering sufficient signal strength for reliable data transmission. This model supports compatibility with Windows 7, Vista, XP, 2000, and LabVIEW Real-Time. The NI 779948-01 offers flexible baud rates ranging from 2 baud to 1,000,000 baud, ensuring precise communication. It achieves over 0.015 percent accuracy for standard baud rates and up to 0.5 percent for nonstandard rates.