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CHAPTER 7 COMMUNICATION PROCEDURE
7
7.2 TCP/IP Communications
7.2.4 Passive open procedure
7.2.4 Passive open procedure
The E71 has the following two connection methods for Passive open.
Under the Passive open method, the open/close processes are performed using the procedures described below,
according to the Ethernet operation setting.
(1) When "Always wait for OPEN (Communication possible at STOP time)" is
selected for the Ethernet operation setting
As the E71 is set to always wait for open, a connection is established when an Active open is requested from the
connected device. This eliminates the need for open/close processing programs on the E71 side.
*1 An open request (SYN) received after the normal completion of an initial process and before the E71 is in the OPEN
request wait status will cause an error, and the E71 sends a connection forced close (RST).
When the open/close processes are performed from the E71 side using a dedicated instruction, even if "Always wait for
OPEN" has been selected for the Ethernet operation setting, the connection will not return to the open acceptance enable
status after the close process is completed.
Unpassive
Performs a passive open process on connections for all devices connected to the network,
regardless of the IP address and port number of the destination device.
Fullpassive
Performs a passive open process on connections for the connected device specified by the
IP address and port number.
After parameter communications, check that the initial process of the E71 is normally completed.
(Initial normal completion signal (X19): ON)
After the initial process is normally completed, the connection enters open enable status and the E71 waits for an open
request from the connected device.
The E71 starts the open process upon receiving the open request (SYN) from the connected device. When the open
process is normally completed, Open completion signal (address: 5000
H
(b0)) turns on and data communications are
enabled.
The E71 starts the close process upon receiving the close request (FIN) from the connected device. When the close
process is completed, Open completion signal (address: 5000H (b0)) turns off and data communications are disabled.
After the internal process of the E71 is completed, the connection returns to the OPEN request wait status.
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3
4
FIN
SYN + ACK FIN + ACK
SYN
ACK
Open status
Open allowed status (closed)
(Active open acceptance enabled)
Closed status
Initial normal completion
signal X19
Open completion signal
(address: 5000
H
)
Power-on
Parameter
communication
completed
Open request signal
(address: 5002
H
)
*1
ACK
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