Monday, February 7, 2011

Specifying the Order of Main Control Programs





Specify the program file number and the order in which the MCPs should be run. This configuration is read before the MCP is executed, if you make change to the configuration screen regarding an MCP, that change takes effect on the next execution of the MCP. You can also change the MCP information through ladder logic by manipulating the status file. The change then takes effect on the MCP next execution.

You can have the same program file number specified more than once as a main control program. For instance, you may want a program to execute frequently and have a higher priority over other programs. If you do not want to use multiple main programs, program your main SFC or ladder program and the processor will execute your main program. You do not need to make any entries on the Processor Configuration screen. The processor enters automatically the main file in the first MCP entry.

Each MCP has an inhibit in the processor status file. You can set these bits to tell the processor to skip over the MCP until the bit is reset. Disable an MCP if you want to hold a machine state temporarily, regardless of transitions, for instance, in machine fault condition. Disabling an MCP can also help to improve scan time, if you know you do not need to run one of your MCP every scan, you can disable it until you need it.

The program scan times for each MCP is stored in the processor status file (S), displaying the previous and maximum scan time. The status file also stores the cumulative of scan time, S:8. The scan time for one complete pass through all MCPs, and the maximum cumulative scan time, S:9. Outputs remain in the state that they were in during the last scan if you disable an MCP.



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