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Registers Theory

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Payload

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

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.

Back to Data_Registers.

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