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MELSEC-F
TROUBLESHOOTING
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NOTE
Depending on the restrictions of the buffers of the local station and external device,
data may be divided for communication.
Data received separately is restored (reassembled) by the Ethernet module to be
communicated using the fixed buffer, etc. The received data is restored
(reassembled) based on the data length in the communication data.
The Ethernet module performs the following processing if data among the
communication data is incorrect.
(1) When communication is performed using fixed buffer (with procedure)
(a) If the data length specified immediately after the subheader is smaller than
the amount of text data received
1) The data immediately following the part of the text data equivalent to the
data length specified immediately after the subheader will be regarded as
the next message.
2) Since the header of each message will be a subheader, the Ethernet
module performs processing according to the code in the subheader.
3) If the subheader contains a code that is not recognized by the Ethernet
module, the Ethernet module will send a response to the external device
notifying it of abnormal completion.
At this point, the Ethernet module returns a response containing a code
obtained by changing the most significant bit of the code processed as
subheader to 1.
For example, if the subheader field of a command is 65
H
, the subheader of
the response will become E5
H
.
(b) If the data length specified immediately after the subheader is larger than the
amount of text data received
1) The Ethernet module waits for the reception of the remaining missing
data.
2) If the remaining data could be received within the time allotted by the
response monitoring timer, the Ethernet module performs processing
according to the code in the subheader.
3) If the remaining data could not be received within the time allotted by the
response monitoring timer, the Ethernet module performs the following
processing.
• Sends the ABORT (RST) instruction to the external device and closes
the line.
• Notifies the PLC side about occurrence of an open error via the open
error detection signal (BFM#28.b6=ON)
• Stores the error code in the open error code storage area. (The error
code is not stored in the error log storage area.)
Sub
Header
Sub
Header
(First data)
(Second data)
Data determined by the Ethernet module
Data sent by an external device
This section is processed as a subheader.
