Edge trigging in ST or SCL

xzen · Jan 12, 2021

What is your best practice for edge trigging in structured text language?

Code:

#condition := (Value1 > 0 OR NOT Tag1) AND Tag2;
IF #condition_positive_edge THEN
    some_code();
END_IF;

ojz0r · Jan 12, 2021

Use the built in functions (IEC 61131-3):
- R_Trig: Rising edge
- F_Trig: Falling edge

AustralIan · Jan 12, 2021

+1 R_Trig

Manglemender · Jan 12, 2021

If you wish to code it yourself then:

IF Condition AND NOT Condition_Memory
Some Code
End IF

Condition_Memory = Condition

Lare · Jan 12, 2021

Jesper's post 9 years ago, same as Manglemenders If condition on ST.

JesperMP said:
Dont think there is a one-shot block for SCL.
But it is trivial to code.

signal_oneshot_ON := signal_input AND NOT signal_mem ; // generate the ON oneshot
signal_oneshot_OFF := NOT signal_input AND signal_mem ; // generate the OFF oneshot
signal_mem := signal_input ; store the status of the input

ndzied1 · Jan 13, 2021

Not sure if it's in all ST packages but in CoDeSys (at least in v3.5) you can set a bit for a positive or negative edge trigger. The 'P' indicates positive edge, for Negative edge it would be an 'N'

Edge trigging in ST or SCL

xzen

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ojz0r

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AustralIan

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Manglemender

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Lare

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ndzied1

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