Yokogawa PR300 Power and Energy Meter - Manual (Page 86)

<Toc> <Ind> <5. Modbus/RTU and ASCII Communication Protocols>
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IM 77C01E01-10E
5.1.4 Configuration of Response
The PR300 receives a command message from the higher-level device. If the received
command message is found to be normal and directed at the station number of the PR300
itself, the PR300 concludes the content of the message to be normal. Thus, the PR300
enters the phase of executing message processing, deciphers the content of the command
message, and processes with the message.
The PR300 does not execute message processing, however, if the received command
message is found to be abnormal. In that case, the PR300 either ignores the received
message or creates a response message telling the received message is erroneous.
After receiving a normal command message and executing a given process, the PR300
creates and sends a response message to which error check data appropriate for the
command function code of the higher-level device is added.
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Responses to Normal Messages
For a loop back function or a function for writing to a single register, the PR300 returns the
received command message as a response message.
For a function for writing to multiple D registers, the PR300 returns part of the received
command message as the response message.
For a readout function, the PR300 adds the read data to the ends of the station number
and function code of the received command message, and returns the message as the
response message.