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Introduction
The IEC61131 PLC Software is a stand-alone package that is part of the WEBCAN Distributed Substation ControlSystem. It allows the user to run programmable logic control (PLC) application fully integrated in a substationcontrol and monitoring system.
The CFE IEC61131 PLC software is based on the InfoTeam PLC kernel which is IEC61131 compatible. PLC programs are created with the InfoTeam OpenPCS Programming Tool and are then downloaded to the PLC Handler running on the WEBCAN CFE. The PLC Handler interprets and executes the PLC program.
A user written PLC program can be monitored, modified and testes with the InfoTeam OpenPCS Programming Tool.
This document covers the following sections:
- General description of the WEBCAN IEC61131 PLC program
- Configuration of the WEBCAN IEC61131 PLC
- Programming the WEBCAN IEC61131 PLC
- The OpenPCS Programming System
Product Components
The WEBCAN IEC61131 PLC application consists of two individual .exe files, namely PLCSystem.exe and
PLCDBHdl.EXE. The two parts exchange data through a common memory area, where the PLCDBHdl part
triggers the PLCSystem par through software interrupt to read and write new data.
PLC System:
PLCSystem.EXE consists of the InfoTeam kernel. It is in charge of cyclically processing and executing the user PLC code and updating user data input and output tables. One PLC program cycle consists of three parts:
- read all inputs from the input table, i.e. copy the inputs into an image table
- execute the user PLC program
- update all outputs to the output table, i.e. copy the outputs from the image table
It is important to note here that because the PLC code is processed between reading inputs and writing outputs, PLC programming loops are not permitted. While the PLC code is in a loop, input and output states are not updated, thus e.g. waiting for an input to change to terminate a loop will not work and end up in an endless loop and watchdog activation, thus a failure of the program.
PLC Database Handler:
The PLCDBHDL.EXE operates as data interface between PLC code and the database, thus other application data. It also schedules the calls to PLCSystem through a software interrupt. The database handler broadcasts changed points to all applications, including the PLC. The PLC DB Handler updates the configured points for the PLC in the input data. Likewise, output points from PLCSystem are passed on to the database handler by PLCDBHDL either as a command or as a message.
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