The communication DFB library is comprised of the following:
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connection management TCP_CNX DFB
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TCP_SEND DFB for transmission of data blocks (8 kb maximum size)
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TCP_RECEIVE DFB for receipt of data blocks (8 kb maximum size)
NOTE: TCP communication DFBs for Premium PLCs use the services from the TCP Open for Premium range to manage TCP connections and to send and receive byte flows on its connections.
The function blocks use the messaging services implemented in the Premium processor. As a result, all the communication blocks can be executed over several PLC cycles. The CPU/module exchange of a datagram is made per PLC cycle.
The execution of function blocks is explicitly maintained. You must program maintenance of the DFB as long as its ACTIVITY bit is active.
NOTE: Do not execute the same DFB instance more than once in the same PLC cycle.
Maintenance of the DFBs is mandatory since all the communication function blocks are executed over several PLC cycles. As soon as the DFB is called, it is restarted for each turn of the PLC cycle as long as its ACTIVITY bit is equal to 1.
