Mitsubishi MELSEC-F User Manual page 106

5 COMMUNICATION PROCEDURE
PLC
Ethernet
module
Ethernet
5 - 32
POINT
This example uses connection number 1 for explanation. Use the corresponding
BFM No. and bits for other connection numbers.
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
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).
Open request signal
(CLOSE processing
execution)
Open completion
signal
Close abnormal processing
FIN
" to the BFM #1602 to 1609 to perform the open
H
1)
2)
FIN is not sent after waiting for the TCP
end timer
3)
At normal completion
FIN
4)
ACK
MELSEC-F
5) 7)
6)
RST
5 - 32