8 Modbus RTU
8.3 Operating mode Modbus RTU
DC1 variable frequency drive 12/13 MN04020003Z-EN www.eaton.com 141
8.3.2 Structure of the slave response
8.3.2.1 Required transfer time
• The time between receiving a request from the master and the response
of the variable frequency drive is at least 3.5 characters (rest time).
• Once the master has received a response from the variable frequency
drive, it must wait for at least the rest time before it can send a new
request.
8.3.2.2 Normal slave response
• If the master request contains a write register function
(function code 06), the variable frequency drive immediately
returns the request as a response.
• If the master request contains a read register function
(function code 03), the variable frequency drive returns the read data
with the slave address and the function code as a response.
8.3.2.3 No slave response
In the following cases, the variable frequency drive ignores the request and
does not send a reply:
• on receiving a broadcast request.
• if the request contains a transmission error.
• If the slave address in the request does not match the variable frequency
drive's address.
• with a CRC or parity error.
• If the time interval between the messages is less
than 3.5. characters.
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The master must be programmed to repeat the request if it
does not receive a response within a specified time.
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