4. Configuration
131
There are no symbols (variables) available in the PLC
configured in the OPC Server. It can happen when
there are no symbols or there isn’t a project loaded on
the PLC.
Finished the process of reading the symbols (variables)
from the PLC configured in the OPC Server. This is a
transitory state during the connection.
After the reading of the symbols (variables) the OPC
Server is running the periodic update of the values of
the available symbols in each configured PLC.
There has been a disconnection with the PLC
configured in the OPC Server.
When the OPC configuration (stored in a
OPCServer.ini file) has a wrong syntax, the variable
value will be this. Generally, this behavior is not
observed for the MasterTool IEC XE maintains this
configuration valid.
Table 4-89. Description of the Communication states between OPC Server and the PLC
The_CommStateOk is a variable of the Bool type that indicates if the communication between the
OPC Server and the PLC is working. When the value is TRUE, it indicates that the communication is
working correctly. If the value is FALSE, for some reason it isn’t possible to communicate with the
PLC.
In addition to monitoring the communication status, the OPC Client can access information on the
quality of communication. The quality bits form a byte. They are divided into three groups of bits:
Quality, Substatus and Limit. The bits are distributed as follows QQSSSSLL in which QQ are the
Quality bits, SSSS Substatus bits and LL limit bits. In this case the QQ bits are the most significant in
the byte, while the LL bits are the least significant.
The value read can’t be used because there’s some
problem with the connection. It’s possible to monitor
the value of_CommState and diagnose the problem.
The quality can’t be defined and may be presented in
the Substatus field.
This value is reserved and isn’t used by the OPC
standard.
The quality is good and the value read can be used.
Table 4-90. Description of the OPC Quality value
Table 4-90 presents the possible quality values. The OPC Server only returns Good and Bad Quality
values. A OPC Client can maintain the quality as Uncertain due to failures in which it can’t establish
a connection to the Server. In case of monitoring of the 8 quality bits directly from the OPC Server,
the Substatus and Limit fields shall be null e a Good Quality will be presented as the value 192 and a
Bad Quality will be value 0.
OPC Server Communication Limits
To communicate with the OPC Server, there are some limitations that must be respected for the
correct functioning of the application. There can’t be more than 20.000 variables configured as
available in the OPC Server for each PLC. Therefore, 20.000 variables is the maximum limit to
communicate with a single PLC.
Furthermore, when configuring the variables to be available in the OPC Server, the quantity of
declared variables in each POU or GVL can’t exceed the limit of 5.000. Table 4-91 presents the
OPC Server configuration limits.
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