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MELSEC-F
TROUBLESHOOTING11
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(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 65H, the subheader of
the response will become E5H.
(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.)
POINT
Designate the actual data size of the text field for "data length" specified in the
application data field of a message sent from the external device to the Ethernet
module.
The Ethernet module never sends text whose size is different from the specified
data length to the external device.
Sub
Header
Sub
Header
(First data) (Second data)
Data determined by the Ethernet moduleData sent by an external device
This section is processed as a subheader.