PXI-8431/4 4-Port RS-485/RS-422 PXI Serial Interface
The PXI-8431/4 is a four-port PXI serial interface module designed for communicating with industrial instruments, embedded controllers, automation equipment and other devices using RS-485 or RS-422 connections.
Each port supports data rates up to 3 Mbps and selectable two-wire or four-wire transceiver operation. The module combines high-speed DMA transfers, independent 128-byte FIFOs and standard operating-system COM-port compatibility for reliable communication in automated test and control systems.
The PXI-8431/4 is a nonisolated interface. Applications requiring electrical isolation between the PXI system and connected equipment should use an isolated serial module or suitable external isolator.
Key Features of the PXI-8431/4
- Four independent RS-485/RS-422 serial ports
- Maximum data rate of 3 Mbps per port
- Supports data rates from 2 baud to 3 Mbps
- Selectable two-wire and four-wire transceiver modes
- Full-duplex and half-duplex communication
- Automatic transceiver control for two-wire networks
- 128-byte transmit and receive FIFOs
- High-performance DMA data transfers
- Multithreaded and multiprocessor system support
- Four front-panel 10P10C modular connectors
- 10P10C-to-DB-9 adapter cables included with the original kit
- Appears as standard COM ports in supported operating systems
- Compatible with NI-Serial and NI-VISA software
- LabVIEW and LabVIEW Real-Time integration
- Compact single-slot 3U PXI module
PXI-8431/4 Technical Specifications
| Product Model | PXI-8431/4 |
|---|---|
| Part Number | 778985-01 |
| Product Type | PXI serial interface module |
| Supported Standards | RS-485 and RS-422 |
| Number of Ports | 4 |
| Electrical Isolation | Nonisolated |
| Maximum Baud Rate | 3 Mbps |
| Supported Baud-Rate Range | 2 baud to 3 Mbps |
| Two-Wire Automatic Control Limit | Up to 2 Mbps |
| Communication Modes | Two-wire half duplex and four-wire full duplex |
| FIFO Size | 128 bytes |
| Data Transfer | DMA |
| Front-Panel Connectors | 4 × 10-position modular jack, 10P10C |
| External Cable Connector | DB-9 male through conversion cable |
| Software Interface | Standard COM ports, NI-Serial and NI-VISA |
| PXI Power Requirement | +5 VDC, 725 mA typical and 1.1 A maximum |
| Dimensions | 100 mm × 160 mm |
| Weight | 140 g |
| Module Format | 3U, single-slot PXI module |
| Availability Status | Discontinued by NI |
PXI-8431/4 Part Number and Connection Accessories
| Item | Part Number | Description |
|---|---|---|
| PXI-8431/4 | 778985-01 | Four-port, nonisolated RS-485/RS-422 PXI serial interface |
| 10P10C-to-DB-9 Conversion Cable | Verify configuration | Converts one front-panel modular jack to a DB-9 male connector |
| Shielded RS-485/RS-422 Cable | Application dependent | Twisted-pair communication cable selected for the required pinout and network topology |
| RS-485 Termination Network | Application dependent | External termination and bias components selected for the cable impedance and network design |
The original four-port hardware kit includes cables that convert the module’s 10P10C modular connectors to DB-9 male connectors. Because the PXI-8431/4 is discontinued, verify that all four adapter cables are present when purchasing a used module.
Confirm the required DB-9 pinout before connecting existing equipment. RS-485 and RS-422 products may use different connector assignments even when they share the same connector type.
Four Independent Serial Ports
The PXI-8431/4 provides four independently configurable serial ports in one PXI slot. Multiple instruments, controllers or multidrop networks can therefore be connected without installing a separate interface for every communication link.
Each port has its own buffering and communication configuration. Test software can use different baud rates, framing parameters and transceiver modes on the four ports according to the requirements of the connected equipment.
RS-485 and RS-422 Communication
RS-485 and RS-422 use differential signaling to provide better noise immunity and longer cable reach than conventional single-ended serial interfaces. These standards are widely used in industrial automation, motion systems, environmental chambers, programmable instruments and embedded equipment.
RS-422 is commonly used for full-duplex point-to-point or multidrop transmission. RS-485 supports bidirectional multidrop networks in which several devices can share the same differential bus.
The PXI-8431/4 supplies the physical serial interface but does not define the application protocol. It can be used with compatible protocols such as Modbus RTU or with proprietary command formats implemented by the connected equipment.
Two-Wire Half-Duplex Mode
In two-wire mode, the transmitter and receiver share one differential signal pair. Devices take turns transmitting, making this configuration suitable for half-duplex RS-485 multidrop networks.
The PXI-8431/4 supports automatic transceiver control, which enables and disables the transmitter at the appropriate point in the communication sequence. Automatic control reduces the need for application software to manipulate a separate direction-control signal.
The automatic two-wire transceiver-control mode supports data rates up to 2 Mbps. Applications requiring communication above this rate should confirm the appropriate transceiver configuration and timing requirements.
Four-Wire Full-Duplex Mode
Four-wire operation uses separate differential pairs for transmitted and received data. This permits simultaneous transmission and reception and is suitable for RS-422 links and four-wire RS-485 systems.
Full-duplex operation can simplify timing when the host and remote device must exchange data continuously. Correctly connect the transmit pair of one device to the receive pair of the other and verify signal polarity before operation.
3 Mbps Maximum Data Rate
Each PXI-8431/4 port supports a maximum baud rate of 3 Mbps. The hardware can also generate custom baud rates from 2 baud through the maximum supported rate, allowing it to communicate with devices that do not use only conventional serial speeds.
Maximum practical distance decreases as baud rate increases. Cable capacitance, characteristic impedance, termination, stub length, grounding and electromagnetic interference all affect communication reliability.
128-Byte Hardware FIFOs
The module provides 128-byte hardware buffering for serial data. FIFOs temporarily store transmitted and received characters, reducing the frequency with which the host processor must service each serial port.
Buffering is especially valuable when several ports operate simultaneously or when the host application experiences short scheduling delays. The driver and application should still use suitable software-buffer sizes for the expected message rate.
DMA Data Transfers
The PXI-8431/4 uses direct memory access to transfer serial data between the interface and host memory efficiently. DMA reduces processor intervention compared with servicing every character individually.
This architecture supports high-throughput applications with several active serial ports. Actual system performance depends on the operating system, driver configuration, message size, application design and connected device response time.
Standard COM-Port Operation
After installation of the supported NI serial driver, each PXI-8431/4 interface appears as a standard serial COM port. Applications can access the ports using conventional serial APIs without directly controlling low-level PXI registers.
Existing software designed for COM-port communication can often use the module after selecting the assigned port number and configuring the required baud rate, parity, data bits, stop bits and RS-485 transceiver mode.
NI-Serial and NI-VISA Support
NI-Serial provides the hardware driver and configuration support required by the PXI-8431/4. NI-VISA supplies a common programming interface for opening the serial resource, configuring communication parameters and reading or writing data.
The module can be integrated into LabVIEW, LabWindows/CVI and compatible text-based programming environments. Before installing discontinued hardware in a new system, verify compatibility between the operating system, PXI controller, NI-Serial version and application software.
LabVIEW Real-Time Integration
The PXI-8431/4 is supported by applicable versions of NI-Serial for LabVIEW Real-Time. A compatible PXI real-time controller can use the four serial ports to communicate with industrial devices while executing deterministic test or control software.
Serial device response time and bus arbitration remain dependent on the connected equipment and protocol. Real-time execution of the host application does not make an asynchronous external serial network deterministic by itself.
RS-485 Network Design
A reliable RS-485 network normally uses a shielded twisted pair with a characteristic impedance appropriate for the selected termination. Termination resistors are generally installed at the two physical ends of the main bus rather than at every node.
Keep branch stubs short, particularly at higher data rates. A linear daisy-chain layout generally produces better signal integrity than a star connection with several long branches.
Bias resistors may be necessary to maintain a known idle state when no transmitter is enabled. Their values should be selected with the termination resistance, number of devices and transceiver loading in mind.
Nonisolated Interface Considerations
The PXI-8431/4 ports are nonisolated. The PXI chassis and connected serial devices must therefore have compatible ground references and common-mode voltages.
Ground-potential differences can cause communication errors or damage equipment. Use an external RS-485 isolator or an isolated interface module when devices are located in different electrical systems, exposed to large ground offsets or connected through long outdoor cable runs.
Typical PXI-8431/4 Applications
- Industrial RS-485 equipment control
- RS-422 instrument communication
- Modbus RTU test systems
- Environmental chamber control
- Programmable power-supply communication
- Motor-drive and motion-controller testing
- Embedded controller validation
- Production-line automation
- Laboratory instrument integration
- Multidrop sensor networks
- Hardware-in-the-loop systems
- Legacy equipment replacement and maintenance
Automated Test Equipment
The four independent ports allow one PXI system to communicate with several serial instruments during an automated sequence. Test software can configure equipment, send commands, receive status messages and record results without external USB serial adapters.
Combining serial communication with PXI measurement instruments provides a unified platform for device configuration, stimulus generation, data acquisition and pass-or-fail evaluation.
Industrial Automation
The PXI-8431/4 can connect a test or supervisory system to industrial equipment such as programmable controllers, motor drives, temperature controllers and remote I/O devices.
For multidrop RS-485 systems, every node must use a unique protocol address when required by the application protocol. The communication settings must match across all nodes sharing the bus.
Environmental Chamber Integration
Many temperature, humidity and vibration systems use RS-485 or RS-422 communication. The module can send setpoints, start test profiles and read status information while other PXI instruments measure the device under test.
Command timeouts should account for the response time of the chamber controller. Long-running operations should be monitored with status queries rather than relying on a single fixed delay.
PXI-8431/4 Troubleshooting
The module is not detected
Confirm that the PXI-8431/4 is fully installed in a compatible PXI slot. Check chassis power, controller communication and installation of a compatible NI-Serial driver. Restart the system and review the hardware status in NI Measurement & Automation Explorer.
The COM ports do not appear
Verify that the serial driver supports the installed operating system and the PXI-8431/4. Check Device Manager or NI MAX for driver errors, resource conflicts or disabled interfaces.
No data is received
Confirm the baud rate, data bits, parity and stop-bit settings. Check that the selected port uses the correct two-wire or four-wire mode and verify the adapter-cable pinout, differential-pair polarity and remote-device configuration.
Communication works only at low baud rates
Inspect the cable type, total bus length, termination resistors and branch-stub lengths. High-speed links require suitable twisted-pair wiring and a controlled bus topology. Reduce the cable length or baud rate to identify signal-integrity limitations.
Characters are missing during heavy traffic
Increase the application receive-buffer size and read data frequently enough to prevent software-buffer overflow. Check whether several ports are transmitting simultaneously and confirm that the program handles partial reads and complete message framing correctly.
A two-wire port cannot transmit
Verify that the port is configured for two-wire RS-485 operation and that automatic transceiver control is enabled when required. Confirm that another node is not holding the bus active and that the network has suitable idle-state biasing.
Data is corrupted or reversed
Check the positive and negative conductors of each differential pair. If the polarity is reversed, the receiver may report framing errors or unusable characters. Also confirm the DB-9 pin assignment rather than assuming that every RS-485 device uses the same wiring.
The link fails when equipment uses different power sources
Measure the ground-potential difference and verify that the transceiver common-mode range is not exceeded. Because the PXI-8431/4 is nonisolated, an external isolator may be required.
PXI-8431/4 Comparison
| Model | Configuration | Best Suited For |
|---|---|---|
| PXI-8431/2 | 2-port RS-485/RS-422 interface | Systems requiring two differential serial ports |
| PXI-8431/4 | 4-port, nonisolated RS-485/RS-422 interface | General four-port industrial serial communication |
| PXI-8431/8 | 8-port RS-485/RS-422 interface | Higher serial-port density |
| PXI-8430/4 | 4-port RS-232 interface | Single-ended RS-232 instruments |
| PXI-8433/4 | 4-port isolated RS-485/RS-422 interface | Systems requiring electrical port isolation |
PXI-8431/4 vs PXI-8431/2
The PXI-8431/4 provides four RS-485/RS-422 ports, while the PXI-8431/2 provides two. Both are appropriate for differential serial communication, but the four-port version connects more independent devices or networks in one PXI slot.
Select the two-port model when only a small number of interfaces is required. Choose the PXI-8431/4 when additional port density will reduce the number of modules needed in the chassis.
PXI-8431/4 vs PXI-8431/8
The PXI-8431/8 doubles the port count from four to eight. The eight-port version is useful in systems containing a large number of serial instruments, while the PXI-8431/4 provides sufficient capacity for smaller systems.
When selecting between them, consider the required connector space, number of adapter cables, software port management and future expansion requirements.
PXI-8431/4 vs PXI-8430/4
The PXI-8431/4 supports differential RS-485 and RS-422 communication. The PXI-8430/4 is intended for single-ended RS-232 devices. These electrical standards are not directly interchangeable.
Select the module according to the interface specified by the connected equipment. A simple connector adapter cannot convert RS-232 electrical signaling into RS-485 or RS-422.
PXI-8431/4 vs PXI-8433/4
The PXI-8431/4 is nonisolated, whereas the PXI-8433/4 family is intended for applications requiring isolated serial connections. Isolation helps protect equipment and reduces ground-loop problems when devices use different ground references.
Choose the PXI-8431/4 for equipment within a controlled common-ground system. Select an isolated interface when the installation has significant ground-potential differences, high electrical noise or additional equipment-protection requirements.
Recommended Related Products
- PXI-8431/2 2-Port RS-485/RS-422 Serial Interface
- PXI-8431/8 8-Port RS-485/RS-422 Serial Interface
- PXI-8430/4 4-Port RS-232 Serial Interface
- PXI-8433/4 4-Port Isolated RS-485/RS-422 Interface
- PXIe-8431/8 RS-485/RS-422 Serial Interface
- View More NI PXI and PXI Express Modules
Selecting the Right PXI Serial Interface
Choose the PXI-8431/4 when the test system requires four nonisolated RS-485 or RS-422 ports, communication rates up to 3 Mbps and selectable two-wire or four-wire operation.
Select a two-port version when fewer connections are required or an eight-port version when port density is the primary concern. Choose an RS-232 module for single-ended equipment or an isolated RS-485/RS-422 module when ground separation and electrical protection are required.
Why Choose the PXI-8431/4?
- Provides four RS-485/RS-422 ports in one PXI slot
- Supports transmission speeds up to 3 Mbps
- Supports both two-wire and four-wire networks
- Provides full-duplex and half-duplex operation
- Uses DMA and 128-byte FIFOs for efficient transfers
- Works through familiar operating-system COM ports
- Integrates with NI-VISA and LabVIEW applications
- Supports industrial instruments and multidrop networks
- Provides a practical replacement for legacy PXI serial systems
Frequently Asked Questions
What is the PXI-8431/4?
The PXI-8431/4 is a four-port PXI serial interface for communicating with devices that use RS-485 or RS-422 electrical signaling.
What is the PXI-8431/4 part number?
The standard NI part number for the PXI-8431/4 is 778985-01.
What is the maximum communication rate?
The module supports baud rates up to 3 Mbps. Its supported programmable range extends from 2 baud to the maximum rate.
Does it support two-wire RS-485?
Yes. The module supports two-wire half-duplex operation with automatic transceiver control. Automatic two-wire control is specified for rates up to 2 Mbps.
Does it support four-wire communication?
Yes. Four-wire mode provides separate transmit and receive differential pairs and can be used for full-duplex RS-485 or RS-422 communication.
Are the four ports isolated?
No. The PXI-8431/4 is a nonisolated serial interface. External isolation may be required when connected equipment has different ground potentials.
Which connectors are on the front panel?
The module has four 10-position modular, or 10P10C, front-panel jacks. Conversion cables supplied with the original kit terminate in DB-9 male connectors.
Can the PXI-8431/4 communicate with Modbus devices?
Yes, when suitable Modbus RTU software is used and the electrical interface, baud rate, framing, addressing and two-wire or four-wire configuration match the connected devices.
Which software supports the module?
The PXI-8431/4 uses NI-Serial and can be accessed through standard COM-port APIs or NI-VISA from LabVIEW and compatible programming environments.
Is the PXI-8431/4 still manufactured?
NI lists the PXI-8431/4 as discontinued and no longer available for new purchase. Used and surplus units may remain available for maintaining existing PXI systems.
Request a Quote for the PXI-8431/4
Contact us for current availability, condition and pricing for the PXI-8431/4 4-Port RS-485/RS-422 PXI Serial Interface. We can also help identify compatible 10P10C-to-DB-9 adapter cables, PXI chassis and alternative NI serial-interface modules.
