function - PLC SFC loop: Can there be more than one token in the loop? -

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i working on plc program using m3 soft crozet millenium 3, question sfc/grafcet functions generally. can sfc loop run more 1 token @ once? way of asking question is, can there more 1 step active @ time in single loop, example, when initial step activated, , activated again before loop completes?

sfcs (black token) petri nets. state can enabled, in parallel other states, in principle.

the trick cause state enabled way; isn't easy arrange happen.

imagine have states sf1, sf2 ... sfn. 1 can arrange sf1 enable sf2 , sf3 (using horizontalbar symbol, called fork in more general literature on parallelism). rather typical. sf2 can enable sf4 enables sf5 ... enabling sfk. can have sfk enable sf1, there's cycle in sequential function net. if can have sf1 enable sf2 enable ... sfk, surely build sfc sf1 enables sf3 , sf2, enables sf1. , if that, can have sf1 enable sf1 , sf3. sf1 manufactures state-enables repeatedly, each triggering sf3.

i can petri nets, anyway. maybe language standard forbids sfcs doing if did so, less powerful petri nets , be, well, dumb.

there's analog of arbitrary networks of sfc states programs gotos. can write gotoful programs hard understand; doesn't mean gotos bad, can misuse anything. (in fact, arbitrary gotos allow 1 build finite state machines, useful if don't have sfcs. people write well-structured code, standard controlled-goto elements (e.g., if-then-else-endif, while end, ...) nested cleanly within on another.

similarly, 1 can build forkful petri nets/sfcs. these hard understand, unless serves significant purpose, 1 tends build sfcs out of cleanly nested fork-... join pairs. in such diagram, don't "one state activated again before loop completes."


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