Chapter 11 RS485 Communication
11-1-4
11.1.3 Communication Process
Communication process
Modbus-RTU communication between the external control equipment and the inverter is
performed by the following process.
(1) A query message is sent from the external control equipment to the inverter.
(2) The inverter waits for the silent interval time and the set time of "RS485 communication
wait time [C078]" after receiving the query message. (The silent interval is a wait time
determined by Modbus-RTU communication and is 3.5 characters long. For Modbus-RTU
communication, 1 character = 11bit data.)
(3) A response message is returned from the inverter to the external control equipment.
(4) After sending the response message, the inverter waits for the completion of receiving
the next query message for the set time of "RS485 communication timeout [C077]". (If
[C077] is 0.00, timeout judgment is not performed.) When a query message is received,
the inverter performs processing according to the message, and then the operation in (2)
is performed. When the timeout occurs, the inverter waits for a query message to be
received and operations according to the setting of "RS485 communication error
selection [C076]".
The communication timeout monitoring starts after the first transmission or reception is
established after the power is turned on or reset. If transmission/reception is not established at
least once, a communication timeout does not occur.
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