Monday, February 7, 2011

Main Control Program of Secure PLC-5





Secure PLC-5 and new platform processors can have up to 16 control programs active in a single PLC-5 processor to control your process. Each of these programs is called MCP (Main Control Program). You can define one main control program for each particular machine or function of your process b using several main control programs. This allows you to separate SFC (sequential function chart) from ladder logic and structure text to subdivide your process and make troubleshooting easier.

For instance, you can specify an SFC program to define the order of events in the process and separate ladder logic and structured text programs to control directly the outputs. Each of them is a main control program. The main control program can be a sequential flow chart, structure text and ladder program in any program file numbered 1 through 19999. You can use any mix of SFC structure text and ladder programs to define up to 16 main control programs. One data table is used by all MCPs.

The main control programs (MCPs) are scheduled to execute in the order which you specified in the processor configuration screen. An I.O image update and housekeeping takes place after each MCP is completed. All MCPs are then repeated in the same order after the last MCP completed. Note that the watchdog set point covers one scan of all MCPs.

If the MCP is ladder program, the program is executed normally, that is, rungs are executed from the first rung to the last, with all counters, timers, jumps and subroutines active). The processor initiates an I/O update, reading local inputs, writing local outputs, reading remote buffers and writing remote outputs to the buffer.

If the MCP is a structured text program, then the program is executed normally. If the MCP is a sequential function chart which is only the active steps are scanned and the transitions from the active steps are being examined.



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