5. CONFIGURATION
VAR_GLOBAL PERSISTENT RETAIN
wGlobalSymbolicPersistentVariable_01 : WORD;
END_VAR
VAR_GLOBAL RETAIN
wGlobalSymbolicRetentiveVariable_01 : WORD;
END_VAR
ATTENTION
To use the retentive and persistent memory flexibly, it’s necessary to use MasterTool IEC XE
2.03 or higher.
5.1.1.3. TCP Configurations
Some of the advanced configurations affect the Nexto Series CPUs supported protocols, as they are connected to the TCP
network layer, as following:
Initial Time-out
ACK Delay
The CPU Nexto, before it responds to any request and as any other Ethernet equipment which uses the TCP transport layer,
demands a communication port opening, in other words, the connection establishment.
The Interface connections quantity is limited and simply does not establish any other connection after its limit is reached.
This can cause problems for the established connections in the server mode, as the connections closing depends on the other
equipment, the client.
The TCP transport layer, responsible for the messages deliver from the origin to destiny, has some parameters with time-
outs, very common in general communication protocols. Such parameters are intended to recover the communication after the
failures are determined. The user must be aware with the time-outs configuration, as it some conflicts might occur with the
values configured inside the application layer. As the TCP configuration is a reference for every instances configured, the time
will be valid if it is smaller than the configured inside a protocol:
Initial Time-out: indicates how long, after the first message transmission, the message must be retransmitted, assuming it
has not been received by the destiny device. At each retransmission the time-out is doubled. The number of transmission tries
is connected to the communication time-out configured inside the protocol. It will be the maximum time before it gives up the
message delivering, when the transmission failure is concretized. In addition, it is important to stress that there’s a maximum
quantity of attempts for the Nexto Series CPUs. This number is set in five attempts before the connection is set up and in three
attempts after that. Every time it reaches the maximum number of retries, the communication attempt process restarted. See
Protocols Configuration section further details regarding time-out parameters utilization as they can be different depending on
the situation. It is important to stress this parameter is only used in the connection setting up, after that it is used statistics from
the last communications to calculate the new time-out.
Example of the initial time-out and the communication time-out parameters inside the MODBUS TCP Server, considering
a not received acknowledge, for the following values: 300 for initial time-out (=300 ms) and 3000 for communication time-out
(=3000 ms):
Figure 43: Initial Time-out and Communication Time-out
Legend:
1. Message transmission instant.
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