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6.4 Using the EN311 Socket Interface
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• Not only must the specified socket TCP port number on the local station not overlap
with any TCP port number already in use in a local station socket, but it also must not
overlap with any UDP port numbers or UDP port numbers used for message
transmission. An error will occur if the port number overlaps.
Error status: Already open ••• 2944(16#B80)
• A connection to the local node itself cannot be established, even if the local node IP
address is specified as the remote node IP address.
• Values in the range 1024 to 65535 can be specified as the object socket TCP port
number for the remote node. An error will be returned if a value outside that range is
specified.
Error status: Port number error ••• 2929(16#B71)
• An error will be returned if the open timeout time is exceeded.
Error status: Timeout ••• 2848(16#B20)
• While the open wait timeout limit can be set to any value in the range 0.1 to 6553.5
seconds or unlimited (infinite), we recommend that the timeout limit be set in the range
0.1 to 32 seconds for active opens.
This is because the EN311 processing continuation time for active open processing is
32 seconds. Even if the timeout limit is set to a value over 32 seconds, once 32
seconds has elapsed, the open processing will never actually be performed. The
system will be in an idle state until the specified time has elapsed.
• Although there will be no error even if you set the timeout time to 32 seconds or more,
do not set the timeout time to unlimited (infinite). If you do so, the socket remains to be
waiting for active open when no connection is established within 32 seconds from the
request. In this case, if you issue a close request to the object socket, the open waiting
state is released and the socket will be able to accept the open request again.
• A connection is established by an active open from another socket applied to a socket
in the passive open state. A connection cannot be established by a passive open from
another socket applied to a socket in the passive open state. Similarly, a connection
cannot be established by an active open from another socket applied to a socket in the
active open state.
• For a socket in the passive open state, it is not possible to open multiple connections
from other nodes by issuing multiple active open requests.
• If an active open request is issued to a nonexistent remote station, an error will occur.
Error status: Transmission complete timeout ••• 5002(16#EC76)
• If you reissue an active open request, you should wait 5 seconds or longer after the
previous timeout. If you reissue it within 5 seconds, the following error will occur.
Error status: LAN controller driver error ••• 2960(16#B90)
• In case of passive open, if you set the remote node IP address to "0.0.0.0", the IP
address of the active open node will not be checked.
• In case of passive open, if you set the remote object socket TCP port number to "0",
the port number of the active open node will not be checked.
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