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MELSEC-F
COMMUNICATION PROCEDURE5
5 - 29
*1 Processing when the open processing is abnormally completed
(TCP)
When opening from the Ethernet module under a normal situation,
if the Ethernet module sends a SYN, the external device returns
an ACK and a SYN.
However, if the Ethernet module sends a SYN and then the
external device returns a RST, the open abnormal completion
(BFM#28 b6) is immediately turned on and open processing ends.
*2 The open status and error code at abnormal end can be confirmed
with the following buffer memory.
• Each connection open abnormal code area of the
communication status storage area
(Connection numbers 1 to 8; BFM#120 to 199)
• Error log area (BFM#227 to 372)
• Error codes stored in the open error code area are cleared when
writing "0001
H" to the BFM #1602 to 1609 to perform the open
operation.
*3 Processing when the close processing is abnormally completed
(TCP) When closing normally from the Ethernet module, the
Ethernet module sends a FIN request and the external device
returns an ACK and a FIN. However, if an ACK and a FIN are not
returned because the external device is faulty, the Ethernet
module forcibly disconnects the connection (sends a RST
message).
POINT
This example uses connection number 1 for explanation. Use the corresponding
BFM No. and bits for other connection numbers.
PLC
Ethernet
module
Ethernet
Open request signal
(CLOSE processing
execution)
Open completion
signal
Close abnormal processing
FIN is not sent after waiting for the TCP
end timer
FIN
ACK
1)
2)
3)
4)
5)
6)
7)
FIN
RST
At normal completion