With the release of version 9.6 last year, netTerrain started supporting the Modbus TCP protocol for network and infrastructure device monitoring purposes in Data Center Infrastructure (DCIM) applications.

What is Modbus?

Modbus is a widely used communication protocol in industrial automation systems that enables data exchange between devices within a network. The Modbus protocol was developed in 1979 by Modicon: it became a popular communications protocol used in industrial automation systems.

Since then, it’s become an industry standard for connecting electronic devices, such as programmable logic controllers (PLCs) and other industrial devices, to enable data exchange and control functions.

Master-Slave Protocol

Modbus is a master-slave protocol, where a “master” device initiates communication with one or more “slave” devices. The master device is typically a central controller that sends requests to read or write data to the slave devices.

In contrast, the slave devices, such as sensors, actuators, or other devices, respond to the requests from the master and provide the requested information or perform the desired action. It operates mainly at the application layer of the OSI stack.

Modbus Communication and Integration in netTerrain

Modbus uses a simple and efficient binary representation – so it’s lightweight and, as a result, works well for resource-constrained systems. The Modbus protocol primarily relies on a straightforward request-response mechanism: this makes it reliable and straightforward when it’s time to troubleshoot. It supports multiple communication interfaces such as serial (RS-232, RS-485) and Ethernet-based protocols (Modbus TCP/IP).

The serial versions are widely used in legacy systems, while Modbus TCP/IP has gained popularity with the increasing use of Ethernet networks in industrial environments. Usually, the serial versions require some sort of Gateway to be integrated into a DCIM system.

netTerrain already supports the integration of Gateways such as the Jace controllers from Honeywell Tridium series. Modbus TCP, on the other hand, feeds the data directly into the network making it possible for netTerrain to read it natively without the aid of additional hardware.

Transmission Modes and Data Types

Modbus supports different transmission modes, including ASCII and RTU (Remote Terminal Unit), each with its own advantages and implementation considerations. ASCII mode transmits data using readable ASCII characters, allowing for easy troubleshooting and debugging, while RTU mode uses binary encoding for improved speed and efficiency.

It also works with multiple data types, including discrete inputs, coils, input registers, and holding registers. Discrete inputs and coils represent digital values (0 or 1), while input and holding registers store analog or numerical values. This flexibility allows Modbus to cater to a wide range of applications, from simple digital control to complex data acquisition and monitoring systems.

netTerrain can read any Modbus signals and map them to properties in netTerrain, for any type of entity including devices for rack and environmental data center monitoring to actuators, sensors, PLCs, CRAC and HVAC units, PDUs, and much more.

Limitations and Considerations

The first thing to consider with Modbus is not that much of a netTerrain limitation perse, but more of a limitation with the protocol itself. Modbus is not really a discovery protocol in the traditional sense (such as SNMP). With Modbus support, netTerrain can update properties for devices that talk Modbus TCP, once those devices are already registered in netTerrain (more on that later).

netTerrain’s support for Modbus centers around Modbus TCP. For serial Modbus, you would need some hardware that is able to read signals from a serial interface (such as RS-485). These devices are usually gateways, such as the Honeywells (Tridium) Jace controllers of the Niagara series, which netTerrain can integrate with. In such architectures using Modbus serial interfaces, the gateway receives the signals and converts the Modbus serial signals into a supported protocol such as Modbus TCP or SNMP.

Also, the netTerrain support for Modbus is limited to SNMP v4.

Now that we have a basic understanding of Modbus we can start digging deeper into the details of how netTerrain can leverage the protocol to update properties of devices and other objects in your diagrams. Stay tuned for the next blog in this 3-part series.

About Jan Durnhofer

As CEO / Product and Engineering Manager, Jan joined Graphical Networks with the purpose of creating the most advanced DCIM and IT visualization company in the market.