Opening a TCP/IP Connection
Original instructions
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Introduction
WARNING
UNINTENDED EQUIPMENT OPERATION
Do not exceed the maximum number of connections. Idle connections that are closed automatically when the limit is reached can affect system performance. See the discussion of closed connections.
Failure to follow these instructions can result in death, serious injury, or equipment damage.
A TCP/IP connection can be opened by a request from:
With a Remote Device
The module prepares for a connection coming from a remote device. When the connection is received, verification of the IP address of the remote machine is done only if an access control check is activated. The test checks to see if the address is on a list of remote machines authorized for connection:
With a Local PLC
When a message is sent out by a communication function while there is no connection to the remote device, the module automatically (internally) opens a connection to the remote 502 port.
Opening a Connection Example
The following figure shows an example of connections. (All communications are over Ethernet TCP/IP.)
In this example, three TCP connections are open for communication between the PC and the PLC stations or between two PLC stations.
Either of two PLCs can open the connection between them.