4. Configuration
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IEC 60870-5-104 Communication Performance
IEC 60870-5-104 Server
The CPU runs the IEC 60870-5-104 Server driver in the same way as other communication Server
drivers, i.e., in background, cyclically, and with a priority below the user application. The task of this
driver specifically runs at every 50ms, and just 1 run cycle of the driver is enough to process and
respond requests. However, due to the fact it is a low priority task, it may not be able to run with the
same frequency, as it depends on the percentage of free CPU and also on the competition with tasks
of other protocols configured on the CPU. The percentage aforementioned is given by the difference
between the MainTask interval and the time that the user application takes to run.
To help in the comprehension of the IEC 60870-5-104 Server driver performance, check below the
result of tests carried out with a IEC 60870-5-104 Client simulator, connected to a HX3040 with a
IEC 60870-5-104 Server driver. The configured database consisted of 4000 digital points and 500
analog points (all with quality and time stamp). The MainTask execution time was 70ms (interval of
100 ms).
Time to complete an
General Interrogation
command: less than one second
Time to transfer 4.000 digital 500 analog events: 25 seconds
System Performance
In cases where the application has only one MainTask responsible for the execution of a single
Program (MainPrg), the PLC consumes a certain amount of time for the task to be processed. Such
period is named Execution Time.
To find out the Execution Time of an application, through the MasterTool Xtorm, use the following
path in the Device (Devices Tree):
Device-> Application-> Task Configuration (Monitor tab), Average Cycle Time column.
Make sure the Cycle Time does not exceed 80% of the interval set in the MainTask. For example, in
an application where the interval is 100 ms, an appropriate Cycle Time is up to 80 ms. This is due to
the fact that the CPU needs time to perform other tasks such as communication processing, display
processing and memory card, as these tasks take place within the range (the remaining 20% of Cycle
Time).
The MasterTool Xtorm can also limit the MainTask Cycle Time by setting the task watchdog in 80%
of the interval.
Even if you are aware of the information, but still want to use such watchdog consistency, select the
Generate error on tasks watchdog consistency
checkbox in the CPU configuration tab. Preferably
though, keep the watchdog time set as 1000 ms, and the mentioned checkbox not selected.
ATTENTION:
In case the user do not follow the 80% and the task execution time of the user exceeds the interval
set for the MainTask, both the display and the diagnosis button may not respond - once its priority in
the system is lower than the user tasks. If you load an error application in the CPU, it may be
necessary to restart it disregarding this application. See Not Loading the Application at Startup.
I/O Scanning
The updating of the inputs and outputs associated to the bus modules is performed primary on the
main task of the RTU, called MainTask, according to the sequence described below:
Inputs Reading
Outputs Writing
User application execution
Wait to complete the interval set for the MainTask