CanaanP

How is logic stored in S7 PLCs?

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Hi, fairly new to Siemens platform but have been around PLCs in general for a long time. I have been told that some programming formats run more efficiently than others within the PLC (ie ST vs LAD). I find this contrary to what I thought I knew before. I was always led to believe that the different IEC 61131 formats were for the user's benefit, and that it's stored as machine code in the PLC (hence the need to compile?). Can anyone point me to a definitive source of documentation for this?

Thanks in advance!

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Hi,

 

Take a look at point 2.4 in this PDF

https://www.industry.siemens.nl/automation/nl/nl/industriele-automatisering/industrial-automation/simatic-controller/modulaire-controllers/simatic-s7-1500/Documents/81318674_Programming_guideline_DOKU_v12_en.pdf

 

Basicly ladder (LAD) and fuction blocks (FDB) will have an intermidiate compiling step during runtime into STL before compiled into machine code.

Siemens SCL (ST) will be compiled directly into machine code, just like STL.

This is changed with their newer PLC's 1200 & 1500.

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Excellent, thank you!

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