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Registers Theory

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Payload may contain lot of information, from networking diagnostics to application data or commands.

The approach shown in this document looks similar to ModBus.


ModBus is a serial communication protocol originally published by Modicon (now Schneider Electric) in 1979 for use with its programmable logic controllers (PLCs).

Simple and robust, it has since become a de facto standard communication protocol, and it is now a commonly available means of connecting industrial electronic devices.

The main reasons for the use of ModBus in the industrial environment are:

  • It has been developed with industrial applications in mind
  • It is openly published and royalty-free
  • It is easy to deploy and maintain
  • It moves raw bits or words without placing many restrictions on vendors

ModBus allows for communication between many (approximately 240) devices connected to the same network, for example a system that measures temperature and humidity and communicates the results to a computer.

ModBus is often used to connect a supervisory computer with a remote terminal unit (RTU) in supervisory control and data acquisition (SCADA) systems.

Many of the data types are named from its use in driving relays: a single-bit physical output is called a coil, and a single-bit physical input is called a discrete input or a contact.

ModBus Limitations

Form the point of view of WINE, ModBus has several limitations:

  • 240 devices are not enough for WINE;
  • WINE network is a more structured than simple master-slave connection;
  • Data types may be much more complex than ones described in ModBus.

In other words, ModBus is just, from the point of view of this document, an inspiring protocol.

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