PXIe-8431/8

PXIe-8431/8 8-Port RS-485/RS-422 Serial Interface Module

Земля PXIe-8431/8 is an 8-port PXI Express serial interface module designed for high-speed communication with RS-485 and RS-422 instruments, controllers, sensors and industrial devices. Each port supports configurable 2-wire or 4-wire transceiver operation for half-duplex and full-duplex communication.

With communication rates up to 3 Mbaud, DMA-based data transfers and compatibility with standard Windows COM-port applications, the PXIe-8431/8 provides a scalable serial interface for automated test, industrial monitoring and hardware validation systems.

Key Features of the PXIe-8431/8

• 8 independent serial communication ports
• Supports RS-485 and RS-422 standards
• Maximum communication rate of 3 Mbaud
• Selectable 2-wire and 4-wire transceiver modes
• Supports half-duplex and full-duplex communication
• DMA-based data transfers
• Multithreading and multiprocessor support
• Appears as standard COM ports in supported operating systems
• Single 68-pin VHDCI front connector
• Includes a VHDCI-to-eight-DB9 serial cable
• PXI Express interface
• Compatible with NI-Serial software

PXIe-8431/8 Technical Specifications

Part Number and Included Cable

Eight Independent Serial Ports

The PXIe-8431/8 provides eight independent RS-485/RS-422 communication ports from one PXI Express slot. Each port appears separately in the operating system and can communicate with a different device using its own baud rate and serial configuration.

This high port density reduces the number of modules required when an automated test system must communicate with multiple controllers, sensors, instruments or embedded devices.

RS-485 and RS-422 Communication

RS-485 and RS-422 use differential signaling, providing better noise immunity and longer practical cable distances than typical single-ended RS-232 communication. These standards are commonly used in industrial equipment, motion-control systems and embedded electronics.

The correct electrical standard, wire configuration, termination, biasing and device addressing must be selected according to the connected equipment and network design.

Two-Wire Half-Duplex Operation

In 2-wire mode, transmitting and receiving share one differential pair. This configuration is commonly used for multidrop RS-485 networks in which multiple devices communicate over the same bus.

Only one device should normally drive the bus at a time. The software and communication protocol must control transmission direction and prevent multiple transmitters from creating bus contention.

Four-Wire Full-Duplex Operation

Four-wire mode uses separate differential pairs for transmitting and receiving. It supports full-duplex communication when the connected device can transmit and receive simultaneously.

This configuration is also suitable for RS-422 point-to-point or multidrop receiver systems. Confirm the pinout and communication mode before connecting the included DB9 cable.

Communication Rates up to 3 Mbaud

The PXIe-8431/8 supports serial communication rates up to 3 Mbaud. The usable rate for a particular installation depends on cable length, cable impedance, termination, network topology, electrical noise and the capabilities of the connected devices.

Lower baud rates may be necessary for long cable runs or multidrop networks. High-speed installations should use appropriate twisted-pair cable and properly placed termination resistors.

DMA and Multithreaded Performance

The module uses DMA transfers to move serial data with reduced host-processor involvement. It also supports multithreaded and multiprocessor applications, allowing several ports to communicate concurrently in larger automated systems.

These capabilities are useful when the test application must continuously monitor multiple serial devices while performing measurements, logging data or executing other test operations.

Standard COM-Port Compatibility

After installing NI-Serial, the PXIe-8431/8 ports appear as standard COM ports in supported operating systems. Existing software written for conventional serial interfaces can often use the module without extensive changes.

Applications can access the ports through NI-VISA, standard serial APIs or other software that supports Windows COM-port communication.

Typical PXIe-8431/8 Applications

• Automated communication with multiple serial instruments
• RS-485 multidrop network testing
• RS-422 device validation
• Industrial controller communication
• Embedded system testing
• Motion controller and drive communication
• Sensor and actuator monitoring
• Electronic control unit validation
• Production-line functional testing
• Data logging from multiple serial devices
• Hardware-in-the-loop test systems
• Laboratory automation

Software and Driver Support

The PXIe-8431/8 requires the NI-Serial driver. NI-Serial provides hardware configuration, COM-port integration and serial communication support for compatible NI software and programming environments.

The module can be used with NI-VISA, LabVIEW, LabWindows/CVI, TestStand, C/C++, C# and other applications capable of communicating through standard serial ports.

Cable and Connection Requirements

The PXIe-8431/8 includes a 1 m cable with one 68-pin VHDCI connector and eight male DB9 connectors. The included RS-485/RS-422 cable has part number 197546-01.

Verify the pinout of the connected equipment before wiring the system. RS-485 and RS-422 equipment does not always use the same DB9 pin assignment, so a custom adapter or cable may be necessary.

Termination and Biasing

RS-485 and RS-422 networks may require termination resistors at the ends of the transmission line to reduce signal reflections. Two-wire RS-485 networks may also require bias resistors to maintain a known bus state when no transmitter is active.

Incorrect or excessive termination can load the network and cause communication errors. Follow the connected equipment manufacturer’s recommendations for termination, biasing, cable impedance and maximum node count.

PXI Chassis and System Integration

The PXIe-8431/8 requires a compatible PXI Express chassis and controller. Suitable chassis options include the PXIe-1092, PXIe-1085 and other NI PXI Express chassis with an available compatible peripheral slot.

The host controller must support the required NI-Serial driver and operating system. Confirm software compatibility before installing the module in an existing PXI system.

Installation and Troubleshooting

Module Is Not Detected

Confirm that the PXIe-8431/8 is installed in a compatible PXI Express slot. Verify the chassis connection, controller operation and NI-Serial driver installation before checking the module in NI Measurement & Automation Explorer.

COM Ports Do Not Appear

Restart the controller after installing NI-Serial and check Windows Device Manager or NI MAX. Confirm that the installed NI-Serial version supports the controller’s operating system.

No Data Is Received

Check the baud rate, data bits, parity, stop bits and flow-control configuration. Verify the DB9 pinout and confirm that the transmitting and receiving differential pairs are connected correctly.

Communication Works Only in One Direction

Confirm whether the connected device requires 2-wire half-duplex or 4-wire full-duplex operation. Check the transmit and receive pair assignments and verify direction control in half-duplex mode.

Communication Is Unstable

Reduce the baud rate and inspect the cable, grounding, termination and biasing. Keep serial cables separated from motors, power converters and other sources of electrical interference.

Ground-Potential Differences Cause Errors

The PXIe-8431/8 is not electrically isolated. If devices operate at substantially different ground potentials or the installation has severe common-mode