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MELSEC-F

COMMUNICATION PROCEDURE

5

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5.6.2 Passive open processing/close processing

This section explains the procedure for opening and closing a connection with the 
Ethernet module via an external device.
The operations of Passive open processing/close processing differ depending on 
whether "Always wait for OPEN" or "Do not wait for OPEN" is selected, as shown in 
this section.

(1) When "Always wait for OPEN" is selected in the operational setting

This is an explanation of (BFM #24 b8: ON) open processing/close processing 
when initial timing settings for Operational Settings are set to be always wait 
OPEN (Communication Possible at STOP).
In this case, sequence programs for open processing and close processing are 
not required because the Ethernet module keeps the connection in the always 
wait for the OPEN status according to the [Open settings] parameter setting.
For detail on the [Open settings] parameter, see Section 5.5, "Open Settings".

*1 An open request (SYN) received after the normal completion of an 

initial processing and before the Ethernet module is placed in the 
open acknowledge enabled status generates an error, and the 
Ethernet module sends a connection forced close (RST).

Open status

Open allowed status
(Listen status)
(Active open acknowledge
 enabled)

Close status

Initial normal completion
BFM#27="0001

H

"

Open completion signal
BFM#20480

Power-on

Parameter
communication
completed 1)

2)

FIN

3)

SYN + ACK

FIN + ACK

Open allowed status
BFM#20482

SYN

4)

( *1)