Introduction to Modbus

Modbus is a serial communication protocol developed by Modicon® (now Schneider Electric) in 1979 for use with its Programmable Logic Controllers (PLCs). In simple terms, it is a method used for transmitting information over serial lines between electronic devices. The device requesting the information is called the Modbus Master and the devices supplying information are called Modbus Slaves. Modbus is used widely by many manufacturers throughout many industries. Modbus is typically used to transmit signals from instrumentation and control devices back to a main controller or data gathering system, for example a system that measures temperature and humidity and communicates the results to a computer. Versions of the Modbus protocol exist for serial lines (Modbus RTU and Modbus ASCII) and for Ethernet (Modbus TCP).

Our Commitment to Modbus

We have been an active and long-time member of the Modbus Organization, a group of independent users and suppliers of automation devices that seeks to drive the adoption of the Modbus communication protocol suite and the evolution to address architectures for distributed automation systems across multiple market segments.

Our implementation of Modbus is amongst the most comprehensive in the industry, with simultaneous support for Modbus client/server and support for Modbus RTU, Modbus TCP, Modbus ASCII networks, and value-added features such as Modbus port expansion and data caching.

Modbus Interoperability

Modbus devices often need to be connected to other networks. For example, in a data center, it might be necessary to integrate the data produced by Modbus-speaking electric sub-meters to an SNMP based data center information management system. Or in a building, Modbus based controllers may be required to present their data to and take supervisory commands from a BACnet or LonWorks based management system. Modbus devices may also need to present their information to a cloud service that speaks XML. 

The FieldServer protocol gateways and routers can connect Modbus devices to various management systems. The FieldServer protocol gateway can also present non-Modbus devices as Modbus TCP devices to a Supervisory Control and Data Acquisition (SCADA) system. integrators and installers use our gateways for their flexibility, reliability, and ease-of-use, while OEMs often incorporate the FieldServer protocol gateway technology into their devices in lieu of doing their own protocol development.


FieldServer protocol gateway and router products from Sierra Monitor can connect Modbus devices to various management systems, and can also present non-Modbus devices as Modbus TCP devices to a Supervisory Control and Data Acquisition (SCADA) system. The products are loaded with the appropriate Modbus drivers along with the other required protocol drivers. Buyers usually order one of the hardware platforms below with the required flavor of Modbus, and specify the other drivers they want loaded on it.

Modbus Converters and Gateways for Integrators

Integrators value the flexibility and ease-of-use offered by the FieldServer protocol gateways because it allows them to complete their integration projects quickly and with low risk. The following products are available to integrators:

Modbus Converters and Gateways for OEMs

OEMs embed the FieldServer protocol gateways with their products as it enables them to become “multi-protocol" aware (without increasing R&D costs), so they can bid on different project specifications. The following products are available to OEMs:

Protocol Drivers

The selected hardware platform is ordered with one or more of the following Modbus protocol drivers:

The gateway is also ordered with one or more of the following protocols depending on what other control networks are being connected to the Modbus network: