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Chapter 7. Modbus RTU Communication Functions
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Overview of Communications
This controller can communicate with a host unit such as a personal computer, PLC, or display unit using the RS-
485 communication Modbus RTU protocol.
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Features
This controller's communication functions have the following features:
•
A 3-wire RS-485 system is used.
•
Up to 31 of C7G controller units operating as slave stations can be connected to
one host unit operating as the master station.
•
Any desired communication data address can be set for almost all parameters of
this controller. Communication data addresses are set at the factory for general
parameters that are used frequently, but they can be changed.
•
Communication data addresses can be set using the SLP-C7 Smart Loader
Package. Up to 200 communication data addresses can be set. They are used also
for Modbus TCP.
•
If the communication specification of the host unit is RS-232C, an RS-232C/RS-
485 communication converter (sold separately) is needed.
Handling Precautions
•
In the case of Modbus communications, the communication data address of
this controller that is set on the host unit may change to [host address -1] in a
communication message.
Example: If the communication data address is set to "1001" on the host unit, it
changes to "1000" in sent communication messages.
Model C7G performs the send/receive process to the communication data
address specified in the communication messages.
Take the host unit's specifications into account when using this device.
•
Because data is not updated for up to 5 s after turning on or restarting this
controller, reading and writing of data by communication during this time will
not be reflected in the controller.
