Chapter 8. Modbus

Table of Contents

Modbus Server
Modbus Client

Among the Siemens proprietary protocol SIMATIC S7 the LOGO!7 supports Ethernet Modbus TCP/IP The LOGO!8 can act as both server or client.

A modbus server (or Slave) offers services as measured data or outputs. It is on its own passive on the net.

A modbus client (or Master) initiates commands on the net and looks for a server that acts.


Registers on LOGO!8 are always 16bit wide. Reading a 32bit wide value from a remote device goes therefore into two holding registers of the LOGO!8 and result in two 16bit values. Little or Big endian and signed values are also an issue.

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