NI GPIB‑140A GPIB Bus Expander

Product Overview

The NI GPIB‑140A is a fiber-optic GPIB bus expander that must be used in pairs. It breaks two core limitations of the native IEEE 488 bus: the maximum 20-meter cable length for a single bus segment and the limit of up to 15 GPIB devices per segment.

The GPIB‑140A converts GPIB electrical signals into optical signals for transmission, delivering galvanic isolation and eliminating ground loop interference. It is ideal for building instrument test systems requiring long-distance, remote deployment or systems with ground potential differences. The GPIB‑140A/2 variant supports a maximum fiber distance of 2 km, while the base GPIB‑140A supports up to 1 km fiber transmission.

Note: This is a legacy NI GPIB hardware product and has been discontinued.

Core Principle

A pair of GPIB‑140A units is installed at the endpoints of two separate GPIB bus segments. The local unit packages GPIB signals and converts them into optical signals, which travel over multimode fiber to the remote GPIB‑140A. The remote unit restores the optical signals back to standard GPIB electrical signals.

It adopts a buffered transfer architecture with built-in FIFO and SRAM buffers to fully preserve GPIB handshaking timings, commands and data. The device is transparent to upper-layer test software, so no code modification is required for existing applications.

The fiber link provides natural galvanic isolation between the two GPIB segments. The two segments can operate at different ground potentials to prevent ground loop current from damaging GPIB controllers and instruments. This is the biggest advantage over conventional copper-based GPIB extension solutions.

Standards & Performance

• Protocol Compliance: ANSI/IEEE 488.1‑1987, ANSI/IEEE 488.2‑1992. Fully supports GPIB management commands including Find Listeners, compatible with IEEE488 instruments from Keysight, Tektronix and other vendors.
• Data Throughput: Supports HS488 high-speed protocol with up to 2.8 MB/s over fiber; 1.1 MB/s under standard GPIB mode.
• Bus Load Expansion: One paired GPIB‑140A link raises the total system GPIB device capacity to 28 units (including the two GPIB‑140A modules themselves).
• Fiber Specifications: Works with NI T7 multimode fiber (850 nm, 62.5/125 μm core). Point-to-point fiber reach up to 1000 m. Multiple GPIB‑140A pairs can be cascaded or deployed in star topology for longer distances and more instrument nodes.

Hardware Architecture

• Onboard Memory: 1 KB SRAM + 512×9 bit FIFO buffer. GPIB logic implemented via FPGA.
• Interfaces: IEEE488 female GPIB connector, dual-fiber port. DIP switches for local / remote mode configuration.
• Power Supply: Integrated power module with AC 100–240 V wide-range input.
• Self-Test: Built-in hardware self-test, triggered on power-up or manually, to quickly diagnose fiber link and GPIB port faults.

Application Scenarios

• Large-scale Test Systems: Separate GPIB controllers in control rooms from instruments in test bays over long distances, such as ATE automated production lines and remote laboratory instrument control.
• Systems with Ground Potential Differences: Test instruments near high-power power supplies, motors and high-voltage equipment. Breaks ground loops and protects GPIB interfaces from surge damage.
• High EMI Environments: Fiber is immune to EMI/RF noise, suitable for EMC testing, power and energy industry measurement & control.
• Distributed Instrument Clusters: Merge multiple GPIB segments across rooms or factories into one logical GPIB bus.

Usage Notes

• Pair Requirement: A single GPIB‑140A cannot operate independently. One unit is set to Local mode and the paired unit to Remote mode.
• Fiber Selection: Only NI T7 series multimode fiber is supported. Single-mode fiber cannot be used.
• Cascading: Multiple GPIB‑140A pairs may be chained to further extend bus distance and device count.
• Software: Fully transparent to NI-488.2 drivers. Existing GPIB programs remain unchanged with no impact on GPIB addressing, triggering and handshaking.

GPIB‑140A vs GPIB‑140A/2

Limitations

• Discontinued legacy hardware. NI no longer ships new units; documentation and legacy drivers remain available.
• Fiber link is point-to-point extension and cannot replace a GPIB controller. A GPIB host controller (PCI‑GPIB, USB‑HS, etc.) is still required in the system.
• Only forwards GPIB protocol. It does not support TCP/IP or other network protocols, differentiating it from GPIB‑ENET Ethernet GPIB gateways.

Compatible Accessories for NI GPIB‑140A

Prerequisite: GPIB‑140A must be deployed in pairs, one Local and one Remote, to form a fiber GPIB extension link. GPIB‑140A/2 is the long-range variant with a 2 km limit and uses T8 fiber.

1. Fiber Cables (Specialized, Non-interchangeable)

GPIB T7 Fiber Cable (P/N: 182805‑xx)

• Compatible with: GPIB‑140A (1 km version)
• Specs: 62.5/125μm multimode, 850nm, ST dual-fiber connector. Available in multiple lengths; suffix xx denotes meters, e.g. 182805‑020 = 20 m.

GPIB T8 Fiber Cable (P/N: 182806‑xx)

• Compatible with: GPIB‑140A/2 (2 km version)
• Specs: 62.5/125μm multimode, 1300nm, ST dual-fiber connector.

Note: T7 and T8 fibers cannot be cross-used. Only multimode fiber is supported; single-mode fiber is prohibited.

2. GPIB Host Controllers (PC-side Master for GPIB‑140A)

GPIB‑140A is only a bus expander and not a controller. It must pair with NI GPIB controllers connected to PC/PXI and works with NI‑488.2 drivers:

• GPIB‑USB‑HS / GPIB‑USB‑HS+ (portable USB, most common)
• PCI‑GPIB / PCI‑GPIB+ (legacy PCI board)
• PCIe‑GPIB / PCIe‑GPIB+ (PCIe desktop card)
• PXI‑GPIB (PXI chassis module)
• PXIe‑8238 (PXIe high-speed GPIB module)
• GPIB‑ENET/100, GPIB‑ENET/1000 (Ethernet GPIB gateway, can stack with GPIB‑140A for dual-layer remote extension)

3. Standard GPIB Copper Cables (Connect GPIB‑140A to Instruments / Controllers)

NI OEM IEEE488 GPIB cables with 24-pin interlocking male-female connectors:

• 763061‑01: 1m GPIB cable
• 763061‑02: 2m GPIB cable
• 763061‑05: 5m GPIB cable

Related Models

• GPIB‑140A: 1km, T7 fiber
• GPIB‑140A/2: 2km, T8 fiber
• GPIB‑140B: Successor of GPIB‑140A with upgraded hardware architecture. Cannot be paired cross-model with GPIB‑140A.

Frequently Asked Questions

Q1: What is the core function of GPIB-140A? Does it have to be used in pairs?

A: The GPIB-140A is a fiber-optic GPIB bus expander built to extend GPIB communication distance, isolate ground loop noise and expand bus device capacity. This unit must be used in pairs; a single module cannot work alone. Set one unit to Local mode and the other to Remote mode to establish valid communication.

Q2: What are the maximum transmission distance and data rate of GPIB-140A?

A: The standard GPIB-140A reaches up to 1000 m with T7 multimode fiber. The GPIB-140A/2 variant supports up to 2000 m with T8 fiber. It supports standard GPIB and HS488 high-speed protocol: 1.1 MB/s under standard mode and up to 2.8 MB/s under HS488 mode.

Q3: Does GPIB-140A require dedicated drivers? What software is compatible?

A: No separate driver installation is required. The hardware is fully transparent to the system. It works with official NI-488.2 drivers, NI-VISA, MAX configuration utility, LabVIEW, Python, C and all common GPIB host environments. Existing test programs run without modification.

Q4: How many devices can be mounted on the GPIB bus after deploying GPIB-140A?

A: A native single GPIB bus segment supports up to 15 devices. After adding one GPIB-140A pair, the total system bus capacity expands to 28 devices (including the two GPIB-140A units), suitable for distributed multi-instrument test systems.

Q5: Can GPIB-140A pair with GPIB-140A/2 or GPIB-140B?

A: Cross-model pairing is not supported. Only identical models can communicate: GPIB-140A pairs only with GPIB-140A, GPIB-140A/2 only with GPIB-140A/2. GPIB-140B is an upgraded successor with different hardware and communication logic and is incompatible with the 140A series.

Q6: What fiber requirements apply to GPIB-140A? Can single-mode fiber be used?

A: It requires official specified multimode fiber; generic fiber cannot replace it. The base model uses T7 multimode fiber (62.5/125μm, 850nm). GPIB-140A/2 uses T8 fiber. Single-mode fiber is forbidden and will lead to communication failure.

Q7: What are the main benefits of GPIB-140A compared to copper GPIB extension?

A: Core advantages include galvanic isolation, noise immunity and long-distance transmission. Copper extension cannot isolate ground potential differences and ground loop current may burn instruments or controllers. Fiber transmission fully isolates ground loops and resists EMI/RF interference for high-voltage, high-power and harsh EMC test environments.

Q8: Can GPIB-140A connect directly to a PC? What additional hardware is needed?

A: It cannot connect directly to a PC. It is a bus extender rather than a GPIB controller. It must work with NI GPIB host controllers such as GPIB-USB-HS, PCIe-GPIB and PXIe-8238 to build a complete communication chain: host controller + fiber expander + test instruments.