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Automatic control function programming manual ladder language

Automatic control function programming manual ladder language

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Pitfall Related to Scanning<br />

Programming in Ladder Language<br />

In the example below, the system reads numerical comparison «Var_3 == 100» before writing «Var_3 = 100» in the<br />

action zone if the conditions of the first rung are satisfied. Write of «Var_3 = 100» and execution of the second rung<br />

are offset by one PLC cycle.<br />

It is therefore important to make sure the scanning order does not affect execution of a programme whose instructions<br />

must be executed during the same PLC cycle.<br />

en-938846/3 5 - 17<br />

5

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