Template:Networking rut manual modbus

Summary

Modbus is a serial communications protocol. Simple and robust, it has since become a de facto standard communication protocol and is now a commonly available means of connecting industrial electronic devices. This chapter is an overview of the Modbus TCP functionality.

Modbus TCP

Modbus TCP provides users with the possibility to set or get system parameters. The Modbus daemon acts as slave device. That means it accepts connections from a master (client) and sends out a response or sets some system related parameter in accordance with the given query.

The figure below is an example of the Modbus TCP window section and the table below provides information on the fields contained in that window:

[[File:{{{modbus_tcp_file}}}]]

Get Parameters

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Modbus parameters are held within registers. Each register contains 2 bytes of information. For simplification, the number of registers for storing numbers is 2 (4 bytes), while the number of registers for storing text information is 16 (32 bytes). The register numbers and corresponding system values are described in the table below:

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* All received/sent data usage values are returned in kibibytes (KiB), which is an ISQ standard accepted by most major standard organizations.
1 kibibyte (KiB) = 2¹⁰ bytes = 1024 bytes
1 mebibyte (MiB) = 2¹⁰ kibibytes (KiB) = 2²⁰ bytes = 1 048 576 bytes

Set Parameters

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The Modbus daemon can also set some device parameters. These parameters and explanations on how to use them are described in the table below:

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* All ON/OFF commands only accept 0 and 1 values, which represent the following:

• 1 - ON
• 0 - OFF