1. Introduction

GPIBEE is a compact, robust, multi-interface GPIB controller designed for laboratory, industrial, and automated test environments. Its solid aluminum housing provides mechanical durability, while a carefully implemented firmware delivers reliable, well-tested operation across all supported interfaces. It combines Ethernet, USB, and UART communication with full GPIB bus control, discovery mechanisms, a built-in web interface, and an internal SCPI command system. On startup, the device automatically selects between Ethernet and USB connectivity based on link detection. The active USB protocol mode (Network, USBTMC, UART++, or Linux GPIB) is configured by the user and does not change automatically.

GPIBEE supports the full spectrum of GPIB-based instruments — from the latest modern laboratory equipment to vintage measurement devices dating back to the 1970s. GPIB (also known as HPIB, the Hewlett-Packard Interface Bus, and standardized as IEEE-488.1 and IEEE-488.2) remains widely deployed across both current and classic test equipment, and GPIBEE is designed to work reliably with all of them. It offers flexible connectivity, robust protocol handling, and a powerful configuration interface accessible through Ethernet, USB, or SCPI.

GPIBEE is intentionally designed to remain isolated from external network resources. It can operate without a gateway, does not issue DNS queries, and never initiates connections to outside servers.

2. Key Features

3. Typical Applications

4. Interfaces

4.1 Interface Overview

4.2 Interface Capability Summary

The following table summarizes the capabilities available across each interface and protocol combination.

4.3 Ethernet Interface

When connected to a network, GPIBEE operates as a LAN-based GPIB controller. Two protocols are available: VXI-11 (supporting multiple simultaneous connections, VXI-11 locking, VXI-11 discovery, VISA compatibility, and SRQ service requests) and the ++ Protocol (identical to USB UART ++ mode, on TCP port 1234).

The Ethernet interface supports DHCP with fallback to a static IP, static addressing without DHCP, mDNS, SSDP, and full GPIB subaddressing. Network parameters such as hostname, IP address, subnet mask, and timing are fully configurable.

Supported Ethernet link modes:

• 10/100 Mbit/s
• Full and half duplex
• Autonegotiation
• Auto-MDI/MDI-X

4.4 USB Interface

GPIBEE provides four selectable USB modes. Only one mode is active at a time. USB supports both High-Speed (480 Mbit/s) and Full-Speed (12 Mbit/s) operation; forcing 12 Mbit/s Full-Speed is possible via configuration.

5. Power Supply

GPIBEE can be powered via USB or Power over Ethernet (PoE). Power source selection is independent of the active communication interface.

6. Indicators and Controls

6.1 LED Indicators

• Green LED: Ethernet operation mode active. Pulses while data is being transferred.
• Orange LED: USB operation mode active. In USBTMC mode, flashes while waiting for a GPIB instrument to be connected. Pulses while data is transferred.
• Both LEDs blink twice on power-up or when switching from Network to USB mode.
• Both LEDs flash alternately when in firmware update mode.

6.2 Button Functions

A button on the bottom side of GPIBEE provides the following functions:

7. Startup Behavior

After power-up, GPIBEE checks for Ethernet connectivity and waits for a configurable time (default: 4 seconds). If no network is detected, it switches to USB mode and enumerates.

When entering USB mode, behavior depends on the selected USB mode:

• USBTMC mode: Waits for a powered GPIB device before enumerating.
• USB Network mode: Enumerates immediately as a network adapter (USB CDC NCM class).
• USB UART ++ mode: Enumerates immediately as a virtual serial port.
• Linux GPIB mode: Enumerates immediately, regardless of whether a GPIB device is connected.

When the device is in USB mode, plugging in an Ethernet cable will cause it to switch back to Ethernet operation.

8. Connecting to GPIBEE

8.1 Web Interface Access

IP Address Assignment

Depending on the interface used, GPIBEE appears under different IP addresses:

Discovery

GPIBEE announces itself via the following discovery protocols (applies to both Ethernet and USB Network mode):

• SSDP — visible in Windows Network Explorer and similar tools
• mDNS — multicast DNS service advertisement
• LXI Discovery — LXI-compatible instrument discovery

Most VISA implementations will automatically detect GPIBEE . You can always connect directly using the device IP address as an alternative.

Opening the Web Interface

Enter the device IP address in any web browser. Examples:

http://192.168.3.2      # USB Network Mode default
http://192.168.1.2      # Ethernet fallback (no DHCP)
http://<DHCP-address>   # Ethernet with DHCP

8.2 VXI-11

GPIBEE supports VXI-11 over both USB Network mode and Ethernet mode. VXI-11 discovery is implemented via VXI-11 discovery, LXI discovery, and mDNS service advertisement of the internal SCPI interface (inst0). Most VISA implementations will automatically detect GPIBEE .

VISA Resource String Format

TCPIP0::<IP>::<instancename>::INSTR

Example:
TCPIP0::192.168.3.2::inst0::INSTR

Instance Names and GPIB Address Mapping

The instance name selects which GPIB device to access:

The allowed primary address range is 0 to 30. The currently configured GPIB controller address (default: 0) cannot be accessed as an instrument. Supported secondary address ranges are 0–30 and 96–126 (96–126 mapped to 0–30 for compatibility).

The inst, gpib, and hpib prefixes are conventional but not mandatory. Any pure alphabetic text can be used as a prefix. However, some VISA implementations (e.g. R&S VISA) only accept the inst prefix, so using inst0 is recommended for maximum compatibility. Instead of a comma separator, an underscore or dash may also be used.

Recommended VISA Implementations

• R&S VISA (lightweight, robust)
• NI VISA (widely used, comprehensive)
• Keysight VISA

Interactive VISA Tools

Most VISA packages include a diagnostic tool: R&S VISA Tester, NI MAX, or Keysight Connection Expert. These tools are useful for auto-discovering VXI-11 devices, interactive SCPI communication, and initial bring-up and troubleshooting.

8.3 USBTMC

GPIBEE implements a USBTMC interface similar to UsbGPIB-V2, providing a 1:1 connection between the PC and a single GPIB device. USBTMC devices are automatically detected by NI VISA, R&S VISA, Keysight VISA, PyVISA, and the Linux kernel USBTMC driver.

AutoID and Resource Naming

The USBTMC resource name can be configured via the web interface or internal SCPI commands. GPIBEE includes an optional AutoID mechanism that automatically queries the connected GPIB device using *IDN?, embeds the instrument identity into the USBTMC resource name, and ensures the VISA resource name reflects the actual instrument. This is extremely helpful when swapping instruments. Only use AutoID with instruments that support the *IDN? query.

Multi-Device Access via USBTMC

The USBTMC standard does not support multiple logical channels. To allow multi-device access, GPIBEE provides an internal SCPI command (SYST:COMM:USBTMC:ADDR) to switch the active GPIB address. Only one device is active at a time and the user must select the correct device before sending commands.

For full multi-device capability with independent logical channels, use USB Network Mode with VXI-11, Ethernet VXI-11, or Linux GPIB. This is the recommended primary connection method for most users when controlling multiple instruments.

8.4 Linux GPIB

Linux GPIB provides an API compatible with NI-488.2 without vendor lock-in and can be controlled from C, Python, and many other programming languages.

Install the Linux GPIB package from https://linux-gpib.sourceforge.io/ and add the following to /etc/gpib.conf (removing any other interface declarations):

interface {
        minor = 0
        board_type = "xyphro_ugc"
        name = "gpib0"
        pad = 0
        master = yes
}

After editing the configuration, call gpib_config to activate the new settings. Use the ibtest application for initial interactive tests with connected instruments.

9. Firmware Update Procedure

1. Enter Bootloader mode (see Section 6.2 — Button Functions: hold button 5 seconds, or hold during USB connect). The same procedure can be used to upgrade to a newer firmware version or downgrade to an older one.
2. GPIBee appears as a USB mass-storage device (similar to a USB flash drive). Both LEDs flash alternately to indicate firmware update mode.
3. Copy the firmware file GPIBee.GFW to the drive.
4. Wait approximately 10 seconds until the file is copied. The device restarts automatically once programming completes successfully.

Firmware files can be downloaded from the product firmware repository: github.com/xyphro/GPIBee (check releases for the latest and previous versions).

The programmed firmware version can be checked at any time by:

• Opening INFO.TXT while in bootloader mode.
• Web interface (Home section).
• Querying the internal SCPI interface: *IDN?

9.1 Firmware Version Syntax

The firmware version consists of three parts: V1.2.2604151622

10. Internal SCPI Command Reference

10.1 General Characteristics

The internal SCPI command interface provides programmatic access to all internal settings. Most settings can also be changed via the built-in web interface — accessible by navigating to the device IP address in any browser — but the SCPI interface allows dynamic configuration from within controlling measurement software.

Access the internal SCPI interface depending on protocol:

• VXI-11 (over USB or Ethernet): Open instance name inst0 .
• ++ Protocol mode: Access GPIB primary address 31 ( ++addr 31 ).
• USBTMC : Requires a custom control-in transfer to enter vendor mode (see below).
• Linux GPIB : The internal SCPI interface cannot be accessed. Use the web server or button shortcut to change settings.
• Button shortcut (non-network mode) : When operating in USB UART++, USB USBTMC, or Linux GPIB mode, press the button once and wait 3 seconds — the device temporarily switches to USB Network mode, making the web interface accessible. Press the button again to return to the previous mode.

USBTMC vendor mode entry (enter internal SCPI via PyVISA):

# Enter internal SCPI mode:
dev.control_in(0xa1, 180, 0, 0, 1)   # bmRequest=0xA1, bRequest=180, wValue=0

# Exit internal SCPI mode:
dev.control_in(0xa1, 180, 1, 0, 1)   # wValue=1
# Or send SCPI command: SYST:COMM:USBTMC:EXITV

General command rules:

• Commands are case-insensitive.
• Commands may be abbreviated: uppercase letters are mandatory, lowercase letters may be omitted. For example, SYST:REB instead of SYSTEM:REBOOT .
• Commands may be terminated with no terminator, <CR>, <LF>, or <CR><LF>. Query responses are sent without termination characters.
• Most settings modify non-volatile memory. A reboot or power cycle is recommended after changes.

10.2 Identification Commands

10.3 System Commands

10.4 Ethernet Configuration Commands

10.5 USB Configuration Commands

10.6 VXI-11 Configuration Commands

10.7 GPIB Commands

11. ++ Protocol Reference

The ++ protocol is a simple, text-based control protocol that allows access to multiple GPIB instruments through a single interface. It is compatible with the Prologix GPIB adapter command set, making migration from Prologix-based setups straightforward. GPIBEE exposes the ++ protocol in two ways:

• Over UART , when USB UART++ protocol mode is selected.
• Over Ethernet or USB Network mode, on TCP port 1234. Ensure the ++ protocol is enabled (default: on).

Connect using any terminal program (to the virtual COM port or TCP/IP port 1234). Commands sent to GPIBEE must be terminated with CR, LF, or CRLF. All commands start with the ++ characters. Any data not starting with ++ is transmitted to the selected GPIB device address.

Data transmitted to the GPIB device must be escaped:

• + (ASCII 43) → ESC + (byte sequence 27, 43)
• CR (ASCII 13) → ESC CR (byte sequence 27, 13)
• LF (ASCII 10) → ESC LF (byte sequence 27, 10)

Data read from the GPIB device is transmitted fully transparent without modification.

Example session:

++addr 5    # Select GPIB device at primary address 5
++auto 1    # Enable auto read-after-write
++read      # Manually trigger a GPIB read (when auto is off)

11.1 ++ Command Reference

12. Technical Specifications

12.1 Electrical and Communication Specifications

12.2 Measured Transfer Performance

The values below are approximate real-world transfer rates measured with actual GPIB measurement equipment. Effective transfer speed depends on instrument response behavior, GPIB handshaking, command framing, protocol overhead, driver implementation, and host software latency.

12.3 Software Compatibility

12.4 Physical Characteristics and Environment

12.5 Package Contents

Acknowledgements

The development of GPIBee was greatly supported by a group of dedicated beta testers who provided invaluable feedback, bug reports, and real-world testing across a wide range of instruments and environments. Their patience and enthusiasm have been essential in shaping this product into what it is today. A heartfelt thank you to all beta testers — your contributions are truly appreciated.

13. Open Source Acknowledgements

GPIBEE builds on a small number of excellent open-source software components. Their contributions are gratefully acknowledged.

All other software modules — including the complete GPIB implementation, the USB stack and class drivers, and the VXI-11 server — are fully custom developments created from scratch for GPIBEE .

No AI-generated code: All firmware and software for GPIBEE were written by hand. No AI-generated source code was used in the development of this product.

14. Release Information

15. Disclaimer and Contact Information

General Disclaimer

The information in this manual is provided "as is" and without any warranties, whether express or implied. We assume no responsibility for errors or omissions, nor for any incidental or consequential damages arising from the use of the product or the information contained herein.

Intended Use

This device is intended for laboratory, industrial, and engineering environments where GPIB-controlled test and measurement equipment is used. It must be operated only by qualified personnel familiar with electrical safety and instrumentation interfaces.

This device is not designed or certified for use in safety-critical applications. Use in life-support, medical, or aviation systems is at the user's own risk and responsibility.

Trademarks

• R&S® is a registered trademark of Rohde & Schwarz GmbH & Co. KG.
• NI™ and National Instruments™ are trademarks of National Instruments Corporation.
• Keysight™ is a trademark of Keysight Technologies, Inc.
• All other trademarks are the property of their respective owners.

Liability Limitation

We are under no circumstances liable for:

• Loss of data
• Loss of production
• Equipment damage caused by incorrect wiring or configuration
• Indirect, incidental, or consequential damages

Liability is limited to the extent permitted by applicable law.

Technical Changes

Specifications, firmware, and documentation may change without notice as part of continuous product improvement. Specifications and performance values may vary depending on configuration, connected instruments, host system, software stack, and operating conditions.

Contact Information

No software is entirely free of defects, and GPIBEE is surely no exception. If you encounter crashes, unexpected behavior, or anything that feels off, we genuinely appreciate hearing about it. Your feedback is highly valued and helps to improve the product.