Fuji Electric FRENIC-VG Series, User Manual

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5.3 Modbus RTU
5-33
Chap. 5
USING ST
ANDARD RS-
485
5.3 Modbus RTU
This communications protocol was created overseas. Where possible, English text is used alongside
the Japanese
.
5.3.1 Message format
The normal format for sending RTU messages is as follows.
1. Query
2. Broadcast
The inverter receives a message with the same station address from the host while in the standby
state. If the message is received normally, the request is processed and a normal response is returned.
If the message is not received normally, an error response is returned. In the case of a broadcast, no
response is returned. There are four types of message: Query, Normal response, Error response, and
Broadcast.
Query
The host sends a message to a single inverter.
Normal response
After the query from the host is received, the request is processed and a normal response is returned.
Error response
An error response is returned if the inverter receives the query but the requested function cannot be
activated. A message indicating the reason why the requested function cannot be activated is sent
with the error response. However, in the case of a CRC error or physical sending error, no response
is returned.
Broadcast
The master uses a "0" address to send a message to all slaves. All slaves that receive the broadcast
message activate the requested function. This process ends with the time out on the master side.
Response
Query message
Host
Inverter
(No response)
Broadcast message
Host
Inverter