The Babel Buster BB3-3101 Modbus to BACnet gateway allows Modbus RTU devices to communicate with BACnet MS/TP devices. Modbus registers may be accessed as BACnet objects, and BACnet objects may be read as Modbus registers. The Modbus to BACnet gateway acts as a translator, or protocol converter, between the two networks.

The Modbus to BACnet gateway may be configured to operate as a Modbus master or a Modbus slave. As a master, the Babel Buster BB3-3101 will continuously poll Modbus RTU slaves according to the register list you provide, and save the register data in BACnet objects. Those BACnet objects may then be read by other BACnet devices. When desired, writing to BACnet objects results in writing to Modbus registers.

BB3-3101 Modbus to BACnet Gateway Functionality

The BB3-3101 is an upgrade to the BB2-3010 Modbus RTU to BACnet MS/TP gateway. The BB3-3101 features a faster processor and more memory, which leads to support for a larger number of BACnet objects (over 1,000 versus 300). In addition, support for state strings for both Binary and Multi-state objects is added in the BB3-3101. The BB3-3101 also features isolation on the MS/TP port.

Feature Highlights
• Connect Modbus RTU Devices to BACnet MS/TP Network
• Connect BACnet MS/TP Devices to a Modbus RTU Network
• Subscribe to COV on Changes from Modbus or BACnet
• Up to 1024 BACnet Objects and 1024 Modbus Registers
• BACnet Input, Value, Output objects for Analog, Binary, Multistate
• Access Modbus Registers as Coil, Discrete, Input, Holding
• MS/TP baud rates: 9600, 19200, 38400, 76800
• FCC, CE Mark, UL 916 Listed, BTL Certified
• Software Included, No Drivers to Buy

Babel Buster BB3-3101 Modbus to BACnet Gateway

Babel Buster BB3-3101 BACnet MS/TP to Modbus RTU Gateway

Order code: BB3-3101
Retail price: $565.00

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Hardened RS-485 Modbus port standard
Isolated RS-485 Modbus port optional
RS-232 Modbus port optional

Control Solutions’ Babel Buster® BB3-3101 is a BACnet MS/TP client/server device that functions as a Modbus RTU master/slave. A large number of BACnet objects gives you flexibility in mapping Modbus registers to any combination of BACnet objects. Packed Modbus registers may be parsed to multiple BACnet objects when reading. Multiple BACnet objects may be packed into a single Modbus register when writing. All standard Modbus register types are supported.

Input objects will poll their assigned Modbus register at the interval you specify, and provide the Modbus data as the Present Value when read. Commandable Output objects are used to write Modbus registers, and will update the Modbus device each time BACnet is updated. The BB3-3101 supports over 1,000 commandable or non-commandable objects.

Value objects will poll their assigned Modbus register at the interval you specify. The content of the Modbus register will be given as the Present Value of the BACnet object when read. The Modbus register is written each time the BACnet Value object is written. The Value object corresponds to the Modbus Holding register.

The BB3-3101 is most often used as a Modbus master, but it can operate as a slave while MS/TP operates as a client (master). This makes it possible to put MS/TP devices on a Modbus network (but does still require an understanding of BACnet). MS/TP data in remote devices is queried and saved locally. The local data may then be accessed by another Modbus master.

The BB3-3101 configuration tool connects to the MS/TP network using the MTX002 MS/TP to USB adapter (if not using a BACnet IP router). This intelligent adapter plugs into your PC's USB port, and offloads the MS/TP token passing from the PC to make it more reliable. The MTX002 allows you to connect your PC to an MS/TP network running at 76800 baud, something not possible with a generic RS-485 port adapter.

The MTX002 functions as an MS/TP device itself. The combination of the MTX002 and configuration tool running on your PC will appear on the network as a discoverable BACnet device. The diagnostic pages in the configuration tool can be used to read and write any objects in any MS/TP device on the network. The configuration pages provide templates for reading and writing the multiple properties per BACnet object that define its Modbus mapping. All configuration parameters exist as properties of BACnet objects which are accessible to any BACnet client. The Control Solutions configuration tool simpy provides a user friendly template for accessing those properties.

BACnet to Modbus Gateway Configuration Tool

The BACnet Gateway Configuration Tool is the most user friendly BACnet gateway configuration tool to date. Connect the gateway to your laptop via a USB to MS/TP adapter (MTX002) or via a BACnet IP router.

Import Modbus register lists formatted as CSV files. Create your register list using any standard spreadsheet program, save as CSV, then import. The tool will then automatically create and assign BACnet objects. You can also start with a BACnet object list, saved as a CSV file, and import the object list. The tool will automatically assign Modbus registers. Or you can specify the complete mapping of BACnet objects to Modbus registers in a CSV file and import that.

You do not need to start with a CSV list. The user friendly tool provides templates to build a complete configuration from scratch. The configuration tool also provides the means to allocate the gateway's object pool to Analog, Binary, or Multi-state type objects, as Inputs, commandable Outputs, or Value objects.

Isolated Modbus Port Option Available

Troublesome ground loops can be created when the Modbus network and MS/TP network ground points are connected together. This loop is broken by using isolated transceivers. The standard BB3-3101 provides 500V isolation between the MS/TP port and gateway common. The gateway power/ground and Modbus port share a common ground.

The BB3-3101-ISO provides additional optional isolation of the Modbus port. There is then 3-way isolation. Both MS/TP and Modbus RTU are isolated from each other and from the power supply input of the BB3-3101-ISO. If the gateway will be powered from a supply that is common to other MS/TP devices, then you will want to use the BB3-3101-ISO so that Modbus RTU is isolated from MS/TP.


BB3-3101 Features

• Read/Write Modbus registers via BACnet objects
     • 1024 BACnet objects, commandable or non-commandable
     • Object allocations are user configurable
• AI, AO, AV, BI, BO, BV, MSI, MSO, MSV objects
• State text string support for binary, multistate objects
• COV subscription support
• BACnet slave is Modbus RTU master or vice versa
• Bidirectional communication between BACnet and Modbus
• Supports Modbus “coils”, input registers, holding registers
• Single or double Modbus registers
• Signed, unsigned, IEEE 754, single bit
• Modbus register mapping configured via object properties
• Modbus registers may be scaled
• Modbus (master) polling interval configurable per point
• Commandable BACnet objects implement priority array
• Standard Isolated EIA-485 transceiver for MS/TP
• Standard Hardened EIA-485 transceiver for Modbus RTU
• Optional Isolated EIA-485 transceiver for Modbus RTU
• Optional EIA-232 transceiver for Modbus RTU
• MS/TP baud rates: 9600, 19200, 38400, 76800
• Modbus RTU baud rates: 1200, 2400, 4800, 9600, 19200, 38400, 57600, 115200
• Powered by 10-30VDC or 12-24VAC 50/60 Hz
• Power Consumption: 0.1A @ 24VDC
• DIN rail mounting, 100mm H x 70mm W x 60mm D
• Pluggable screw terminal blocks
• Operating temperature -40°C to +85°C
• Humidity 5% to 90% non-condensing
• Listed to UL 916 and (Canadian) C22.2 No. 205-M1983
• BTL Certified, FCC, CE Mark


• Modbus Tutorial
Introduction to Modbus, including function codes, exception codes, register numbering.

• BACnet Tutorial
Introduction to BACnet

BB3-3101 Video Library

Watch these videos for an introduction to configuring the gateway.

Introduction to BB3-3101 Gateway

Configuring the BB3-3101 as a BACnet Device

Mapping Modbus Registers to BACnet

Mapping BACnet Objects to Modbus

CSV to XML Conversion Tool

Babel Buster Configuration Builder

The Configuration Builder software available for use with the web based gateways (such as BB3-7301) is not needed for the BB3-3101 because CSV import capability is already included in the configuration tool for the BB3-3101 gateway.

The CSV import simplifies the process of creating or changing a large number of entries because you can use any standard spread sheet program to manipulate the content of one or more CSV files, and then import that configuration to be loaded into the gateway. If the gateway will be reading a long list of Modbus registers, for example, you can sometimes just copy a list of registers from another source, paste into a simple text file, and import that into the spread sheet program. Then add a header line to label the content, add a handful of additional columns, and you quickly have most of a complete configuration. Very often, the only thing that changes from one line to the next is the register number. The other entries can be quickly made by entering once and using the spread sheet program's "fill down".

Get the Tool Now!

This tool is free and available for download now. Unzip and run the BB3-MSTP-Modbus_Setup.exe file. Open the program, and click the help icon (blue question mark in upper left corner) to access the user guide.

Download the Babel Buster Configuration Tool here.

CSV to XML Conversion Tool

Configuration Service

Need even more help with your network gateway configuration task? We can do the configuration for you, or at least give you a big head start. We are working on building a library of configuration files for commonly used devices. If yours isn't already in the library, we will add it. To get started, open a support ticket and attach a copy (typically a .pdf document) of whatever documentation you have for your device. In addition, provide a list of the registers or objects you want to read or write. Of course, you can also start by asking if we already have that device in our library. If you have a proprietary application that you do not want included in our library, you can hire us at a very reasonable rate to do custom, proprietary configuration work for you, too.

Our most extensive technical support is provided by the same engineering staff that developed the products. Your personal attention from this staff is available via the support ticket system.

No user/password is required to open a new ticket. Once you open a ticket, you will immediately receive an email with your ticket number. Your ticket number becomes your login to review your ticket(s) later. Click the Support Ticket icon anywhere you see it. (If you do not get an email with your ticket number, within minutes, check your junk folder, spam settings, etc, and try again if necessary.)

 Open a Ticket