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Modbus™ Plus <=> Modbus / TCP Ethernet Bridge




Hot Modbus Plus Video

Download the WMV version

Download the WMV version

Click here for a companion manual for the MEBII setup video.


The MEBII is a Unity compatible, fully functional, bi-directional Modbus Plus to Ethernet bridge. Devices on either network can access devices on the other network. This network traffic can be programming commands as well as I/O and register data. In addition, the MEB-RT can act as:
  • DIN rail mount
  • - Easy to install
  • 24VDC Operation
  • Dual Cable Modbus Plus
  • - Also works with single cable systems
  • Built-in Web Server for configuration
  • 100BaseT RJ45 Ethernet port
  • Optional second 100BaseT RJ45 Ethernet port
  • Two Isolated serial ports
  • - each selectable between RS-232 (RJ-45) and RS-485 (5-position screw terminal)
  • LCD Dispaly and keypad
  • - Easy setup from the front panel
  • Automatic Modbus/TCP and Modbus serial routing table configuration
  • Data Concentrator
  • - Serial Auto-transfer, MB+ Global data, E-Peer, Modbus/TCP I/O Scanner
  • Ethernet Gateway or MUX
  • - Modbus (RTU or ASCII, Master or Slave), SY/MAX, RNIM, PNIM
  • Legacy SY/MAX support
  • - SY/MAX 802.3 Ethernet, SY/MAX serial, Net-to-Net, PNIM, RNIM
  • Hot Modbus Plus - Fully Redundant paired operation

The MEBII replaces all previous versions of the MEB, MEB-TCP, and MEB-RT. It has at least one 100BaseT RJ45 Ethernet port and a redundant-cable Modbus Plus port. The Modbus Plus port works with single- or redundant-cable Modbus Plus networks.

Front Panel Operation

The MEBII includes a 5-button keypad and a password protected LCD screen. Nearly all Etherent, MB+, and serial port settings may be inspected and modified from the front panel. View statistical information about each of the ports, check firmware versions, even reset the unit to factory defaults without a PC.
Set the IP Address Default Screen Main Menu Config Menu Comms Settings Ethernet Settings IP Address Screen

Set the MB+ Drop Default Screen Main Menu Config Menu Comms Menu MB+ Drop Setting

View other MB+ nodes Default Screen Main Menu Information Menu MB+ Drops

Modbus Router

The MEBII can route messages between Modbus/TCP Ethernet, Modbus Plus, and Modbus Serial (RTU or ASCII); all at the same time. The Ethernet port may be a client and server. The serial ports may be connected to masters or slaves. Any master can communicate with any slave on any other port. These masters may be a programming package such as Unity Pro, Concept, or ProWORX.
Modbus Router

Web Server

The MEBII includes a Web Server for configuration and troubleshooting using a standard browser.
IP Settings Port 1 Settings

Hot Modbus Plus

A pair of MEBII units may be configured for "Hot Modbus Plus" operation for high availability bridging systems thus eliminating any single point of failure.
Hot MB+

Legacy SY/MAX Operation

The MEBII supports legacy Square D SY/MAX communication including Ethernet and serial. The Ethernet port may be configured to operate in a combined Modbus/TCP and SY/MAX mode providing high speed bridging between Quantum NOEs and Model 650 and 450 PLCs. SY/MAX serial, PNIM, Net-to-Net, and RNIM protocols are all supported to tie in older SY/NET equipment with a newer Modbus system.

Ordering Information

The MEBII is available as:
     * MEBII-001     non-RoHS with 2 isolated RS-232/RS-485 ports, 1 Dual Cable Modbus Plus port, 1 Ethernet port (RJ45 100BaseT connector).
     * MEBII-201     non-RoHS with 2 isolated RS-232/RS-485 ports, 1 Dual Cable Modbus Plus port, 2 Ethernet ports (RJ45 100BaseT connectors).
     * MEBII+001     RoHS with 2 isolated RS-232/RS-485 ports, 1 Dual Cable Modbus Plus port, 1 Ethernet port (RJ45 100BaseT connector).
     * MEBII+201     RoHS with 2 isolated RS-232/RS-485 ports, 1 Dual Cable Modbus Plus port, 2 Ethernet ports (RJ45 100BaseT connectors).

Related Equipment

The MEBII has the following equipment available:
     * MM1     RS-232 cable for connecting to a 9-pin PC serial port.
     * MU7     RS-422 cable for connecting to a 9-pin SY/MAX serial port.
     * TR121ST     120VAC (US) wall mount power supply.


Warranty / Manual: The MEBII manual is located on the Niobrara website. The module carries a one year warranty from the date of shipment. During the warranty period, free firmware upgrades are available. See Niobrara's Standard Terms and Conditions of Sale for additional warranty information.

Dimensions: DIN rail mount 4.4" wide by 4.4" tall by 3.5" deep. Approximately 1.2 pounds net.

Power Requirements: 9-30VDC 6W - 3 position removable connector is provided.


  • Module: LCD with backlight and two red LEDs for error
  • Serial Ports: Transmit and Receive for each port
  • Ethernet: Link/Activity, 10/100
  • Modbus Plus: Active, Channel A Error, Channel B Error

Modbus Plus Ports: Front mounted dual cable Modbus Plus port with two DB9 female connectors with screw-lock posts. Standard MB+ pinout. Global Data compatible.

Ethernet Ports: 10/100BaseT port with RJ45 connector on bottom of unit. Modbus/TCP and/or SY/MAX 802.3 protocols. E-Peer compatible. Web Server. MEB+201 includes two 100BaseT ports, RST supported copper ring or daisy chain connection.

Serial Ports: Two isolated ports selectable between RS-232 (RJ45 connector) and RS-485 (5 position removable screw terminal is provided). Independently configurable for baud rate, data bits, parity, stop bits, and protocol. RS-485 mode is 2- and 4-wire compatible.

Serial Port Modes: Each serial port can independently operate in any of the following modes: Modbus (RTU or ASCII, Master or Slave), SY/MAX; Net-to-Net; Peripheral; PLogic; Multidrop; IDEC; Gateway; Transparent; Share; PNIM; RNIM (Master or Slave); Transfer; Chevron. Dual slave.

Setup Registers: Module configuration is stored in internal registers and is compatible with older MEB-RT models. These setup registers can be accessed through any of the MEB's ports (in most modes). Configuration is restored from FLASH memory after a power cycle.

Environmental:Operating conditions are 0-50C; humidity up to 90% noncondensing; pressure altitude -200 to +10,000 ft MSL.

Effective 8 January 2021 - Specifications subject to change without notice.