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Automating Manufacturing Systems - Process Control and ...

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plc advanced functions - 16.21<br />

S:FS<br />

L<br />

STB<br />

U<br />

STA<br />

STA<br />

STB<br />

STC<br />

STA<br />

STB<br />

STC<br />

U<br />

JSR<br />

sta_transitions<br />

JSR<br />

stb_transitions<br />

JSR<br />

stc_transitions<br />

L<br />

L<br />

L<br />

STC<br />

light_0<br />

light_1<br />

light_2<br />

Figure 16.20 The Main Program for the State Diagram (Program File 2)<br />

The ladder logic for each of the state subroutines is shown in Figure 16.21. These<br />

blocks of logic examine the transitions <strong>and</strong> change states as required. Note that state STB<br />

includes logic to give state C higher priority, by blocking A when C is active.<br />

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