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FINS/TCP Method Section 7-4
• If there is no response from the client when the keep-alive function is in
effect.
• If a command other than FINS FRAME SEND or CONNECTION CON-
FIRMATION is received from the server, the connection will close after the
FINS FRAME SEND ERROR NOTIFICATION command is sent.
Even if the connection is closed at the FINS/TCP client, requests continue to
be made to the FINS/TCP server every few seconds to open a connection.
Note After the Ethernet Unit power is turned ON or the Unit is restarted, the IP
address for the connection used as the FINS/TCP client is the remote IP
address set under the FINS/TCP Tab in the Unit Setup.
To dynamically change the remote IP address (i.e., during CPU Unit opera-
tion), execute the CMND(490) instruction in the ladder program and send a
FINS command (FINS/TCP CONNECTION REMOTE NODE CHANGE
REQUEST: command code 27 30 hexadecimal) to the Ethernet Unit.
Automatic Allocation
of FINS Node
Addresses
When the FINS message service is used, a FINS node addresses must also
be allocated in the host application for communications. The FINS node
addresses used by the host application are normally allocated in advance
using fixed allocations. When the FINS/TCP procedure is used, however, the
FINS node addresses used by the host application can be allocated automat-
ically at the Ethernet Unit.
■ Automatic Allocation Procedure
When exchanging FINS node addresses, node address 0 (node address not
set) is used for the client. At the server that receives the information, a num-
ber from the automatically allocated node addresses (default: 239 to 254)
controlled by the server that has not established a connection is automatically
allocated, and the FINS node address is sent to the client.
After exchanging the FINS node addresses, the client uses the allocated node
address (default: 239 to 254) to create FINS frames (substituting the value
allocated in SA1 of the FINS header).
Personal computer
(Client)
Ethernet Unit
(Server)
Example:
IP address C
FINS node address 0
Example:
IP address S
FINS node address B
Passive open
Connection established
FINS node addresses exchanged
Normal data communications
Connection request (C→S)
Active open
Connection established
Local node address sent
Remote node address received
FINS frame sent
Full duplex communications
FINS node address 0 sent
Connection established
Remote node address received
Local node address sent
FINS frame sent
FINS node address sent
Client: A
Server: B