Modbus protocol disadvantages & limitations

In this article, we will overview some of the limitations and disadvantages of the common protocol called Modbus. We at MindoLife are aware of these limitations and created our system to solve these problems and limitations.

What is Modbus?? 

Modbus is a data communications protocol originally published by Modicon (now Schneider Electric) in 1979 for use with its programmable logic controllers (PLCs).

Modbus has become a de facto standard communication protocol and is now a commonly available means of connecting industrial electronic devices (By Wikipedia). Modbus is prevalent in industrial environments because it is openly published and royalty-free.

It was developed for industrial applications, is relatively easy to deploy and maintain compared to other standards, and places few restrictions – other than the datagram (packet) size – on the format of the data to be transmitted. Modbus uses the RS485 or Ethernet as its wiring type. Modbus supports communication to and from multiple devices connected to the same cable or Ethernet network. For example, a device that measures temperature and a different device to measure humidity communicate the measurements to a computer.

Modbus is often used to connect a plant/system supervisory computer with a remote terminal unit (RTU) in Supervisory Control and Data Acquisition (SCADA) systems in the electric power industry.

Many data types are named from industrial control of factory devices, such as Ladder logic, because of their use in driving relays: A single physical output is called a coil, and a single physical input is called a discrete input or a contact.

Modbus protocol disadvantages:

However, the Modbus protocol has some advantages that become critical with the latest technology jumps, especially the IoT technologies, which provide some solutions that give it an advantage on the Modbus protocol.

Modbus protocol disadvantages include the following:

1. Modbus is restricted to addressing 247 devices on one data link, limiting the number of field devices connected to a master station (Ethernet TCP/IP proving the exception).
2. Modbus was designed in the late 1970s to communicate to programmable logic controllers; the number of data types was limited to those understood by PLCs at the time. Large binary objects are not supported.
3. There is no standard method for a node to find the description of a data object, i.e., finding a register value representing a temperature between 30◦ and 175◦.
4. Since Modbus is a master/slave protocol, there is no way for a field device to “report by exception” (except over Ethernet TCP/IP, called “open-mbus“)
5. No security against unauthorized commands or interception of data
6. Transmissions must be contiguous, limiting the types of remote communications devices to those that can buffer data to avoid gaps in the transmission.
7. A tremendous amount of configuration and programming required
8. The protocol is not standard in the SIMATIC family

MindoLife provides unique IoT Controllers that connect and replace all Modbus wired networks and can manage an unlimited amount of Modbus supported devices.
It’s fully secured, scalable, and with broad wireless coverage. Contact us for more info.