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Additional Guidelines for IEC Hot Standby
156
840 USE 106 00 January 2003
Configured State
RAM Registers,
Continued
With Concept 2.2 the mirror buffer does not exist anymore, but it’s still worth not
having significantly more state RAM references configured than actually used.
The actual use of state RAM references should concentrate on I/O purposes only
and not on storing some application data, just to make it accessible for a SCADA
system. The better way would be to use any kind of application related data, which
includes everything except I/O points, pure IEC variables (non located variables).
The connection to the SCADA system can then be accomplished more easily with
an OPC (OLE for Process Control) server, that accesses certain application data by
name and not by location. This method of SCADA connection is very flexible and
reliable and saves state RAM, which is good for IEC Hot Standby applications.
Efficient Use of
IEC Application
Data
There is one thing that can reduce the IEC application data consumption better than
anything else:
Program only what’s really necessary to control a particular process.
When learning about IEC compliant programming and the different EFBs in the
different libraries, concentrate on which EFBs not to use. This will help you reduce
the size of an application to the necessary minimum.