Modbus

Modbus Gateways, Converters, & Protocols

Modbus Solutions from FieldServer Technologies

FieldServer has an extensive protocol library including many Modbus protocol drivers and Modbus Gateways.

FieldServer technology enables communication between machines and devices that use non-compatible data protocols, and FieldServers can be found in industrial plants and commercial buildings around the world. Contact Us to learn more about FieldServer solutions.

Modbus to BACnet Gateway & Converter

QuickServer LonWorks BACnet/IP Cost effective, easy-to-use BTL Marked gateway to interface Modbus TCP (Modbus TCP/IP) and BACnet IP. QuickServer can act as a Modbus Client or Server and follows the Modbus-IDA specifications. In order to meet the needs of all Modbus users, the QuickServer Modbus TCP driver uses three models, 1) Modicon_5digit where addresses are defined in the 0xxxx, 3xxxx or 4xxxx format with a maximum of 999 registers that can be mapped of each type, 2) ADU Application Data Unit address where addresses of each type are defined in the range 1-65536, or 3) PDU Protocol Data Unit address where addresses of each type are defined in that range 0-65535. QuickServer can emulate BACnet as either a server or client. BACnet COV support for fast data communication while reducing traffic over a BACnet network. QuickServer supports multiple BACnet data types.

Modbus to LonWorks Gateway & Converter

Proven, cost-effective, LonMark Certified gateway interfacing Modbus RTU and LonWorks. QuickServer can act as a Modbus Client or Server and follows the Modbus-IDA specifications. In order to meet the needs of all Modbus users, the QuickServer Modbus TCP driver uses three models, 1) Modicon_5digit where addresses are defined in the 0xxxx, 3xxxx or 4xxxx format with a maximum of 999 registers that can be mapped of each type, 2) ADU Application Data Unit address where addresses of each type are defined in the range 1-65536, or 3) PDU Protocol Data Unit address where addresses of each type are defined in that range 0-65535. LonWorks device can be used with explicit and/or implicit addressing and can be bound to a maximum of 15 other LonWorks nodes. The QuickServer can handle a maximum of 250 explicitly addressed nodes. The QuickServer currently supports a default of 63 network variable aliases to avoid network variable connection constraints.

Modbus to KNX Gateway & Converter

A QuickServer KNX Protocol gateway can act as a Modbus client or server, and follows the Modbus-IDA specifications. In order to meet the needs of all Modbus users, our KNX device uses three models: 1) Modicon_5digit, where addresses are defined in the 0xxxx, 3xxxx, or 4xxxx format with a maximum of 999 registers that can be mapped of each type; 2) ADU (Application Data Unit) address where addresses of each type are defined in the range of 1-65536; or 3) PDU (Protocol Data Unit) address where addresses of each type are defined in the range of 0-65535.

FS-B35 Series FieldServer Modbus TCP to EST3 Fire Alarm Control Panel

LonWorks GatewayA multiport, high-capacity, feature-rich, proven gateway interfacing Modbus TCP and EST3. The FieldServer Gateway can act as a Modbus Client or Server and follows the Modbus-IDA specifications. In order to meet the needs of all Modbus users, the QuickServer Modbus TCP driver uses three models, 1) Modicon_5digit where addresses are defined in the 0xxxx, 3xxxx or 4xxxx format with a maximum of 999 registers that can be mapped of each type, 2) ADU Application Data Unit address where addresses of each type are defined in the range 1-65536, or 3) PDU Protocol Data Unit address where addresses of each type are defined in that range 0-65535. The FS-B35 series Modbus - EST3 Gateway utilizes the EST3 External Communications Protocol (ECP) in which FieldServer acts as an EST3 client supporting Gateway Type II and Type III, using EST3 read operations for report service and delta service and Write Operations for command service.

Modbus Port Expander

The FieldServer Modbus Port Expander connects Modbus RTU devices to Modbus TCP/IP seamlessly and quickly. Once the Serial & Ethernet ports are configured through the Web interface on the FieldServer, the FieldServer will essentially be a “pass through” for Modbus TCP/IP traffic to Modbus RTU devices. Up to 32 Modbus RTU devices can be connected to the RS-485 port on the FieldServer. To access the web configuration page in the FieldServer simply type in the IP address of the FieldServer into your web browser. Check out the Modbus Port Expander page for instructions and more information.

Modbus Protocol

Modbus is an application layer messaging protocol that provides client/server communication between devices connected on different types of buses and networks. Modbus is available as a serial protocol - Modbus RTU or MModbusodbus ASCII, an Ethernet protocol - Modbus TCP, or a fieldbus protocol - Modbus Plus. Also certain manufacturers have modified the standard Modbus protocol to meet their specific needs such as Modbus Daniels, Modbus Omniflow and Modbus TekAir. Modbus has been the industry’s defacto standard since 1979 when Modicon introduced the protocol in its PLCs. Modbus continues to enable millions of devices worldwide to communicate and it continues to grow in most industries.

Modbus is a request/reply protocol and offers services specified by function codes. These function codes are elements of the Modbus request/reply protocol data units (PDUs).

There are three categories of Modbus:

  • Modbus Serial – either Modbus ASCII or Modbus RTU
    • Modbus RTU – each eight-bit byte in a message contains two four-bit hexadecimal characters, main advantage is its greater character density allows better data throughput than ASCII for same baud rate.
    • Modbus ASCII – each eight-bit byte in a message is sent as two ASCII characters, main advantage is that it allows time intervals of up to one second to occur between characters without causing an error.
    • Other Serial Modbus – several manufacturers have made modifications to the Modbus protocol to meet their specific application needs, these would include a Modbus Daniels, Modbus Omniflow, Modbus Tek Air and others.
  • Modbus TCP – Modbus over TCP/IP Ethernet network.
  • Modbus Plus – a peer-to-peer industrial network in which any controller can initiate transactions with the other controllers.

Modbus Data Model

Modbus Controllers communicate using a master-slave technique, in which only one device (the master) can initiate transactions (queries). The other devices (the slaves) respond by supplying the requested data to the master, or by taking the action requested in the query. Typical master devices include host processors and programming panels. Typical slaves include programmable controllers.

The master can address individual slaves, or can initiate a broadcast message to all slaves. Slaves return a message (response) to queries that are addressed to them individually. Responses are not returned to broadcast queries from the master.

The Modbus protocol establishes the format for the master's query by placing into it the device (or broadcast) address, a function code defining the requested action, any data to be sent, and an error-checking field. The slave's response message is also constructed using Modbus protocol. It contains fields confirming the action taken, any data to be returned, and an error-checking field. If an error occurred in receipt of the message, or if the slave is unable to perform the requested action, the slave will construct an error message and send it as its response.

Modbus Protocol Solutions from FieldServer Technologies

Links

Modbus.org - A community for Modbus Users by Modbus Users

Modicon - Site of the original inventors of the Modbus protocol, Modicon, now known as Schneider Automation. Useful Modbus protocol-related information can be found here.