SFC46

Hi dear expert

As you know by calling SFC46 in a program CPU goes to stop mode.

Isn't there any other way to making stop mode by using programming?

Can anyone explain what is the concept behind this block? and is it possible to write a program ,which act like that?(especially with SCL language)

Thanks

Please refer below topics which may help you.

Why to use SFC46 (STP)?

question to STL

Check FB/FC code at runtime?

MJ90

Isn't there any other way to making stop mode by using programming?

That's easy. Remove all errors catching OBs and do something stupid. Like division by 0. 

jacek d

 

MJ90

Isn't there any other way to making stop mode by using programming?

That's easy. Remove all errors catching OBs and do something stupid. Like division by 0. 

 Would you please give an example?

dchartier

Hello MJ90;

You want an example of what exactly?

Divide by zero? This is a forbidden instruction in computers (and PLC) systems, since the result will be an infinite., non-calculable number. The consequences of a divide-by-zero operation on a PLC will be a major fault, and running an infinite loop from which the CPU cannot recover by itself. The operating system of the CPU will intervene to protect the PLC by calling a Stop operation which will help reset the PLC memory areas.

See the article in Wikipedia for more information and the extract below.

https://en.wikipedia.org/wiki/Division_by_zero

There are many other operations and circumstances that can affect adversely the PLC operations, and the reaction to a major fault will generally require a Stop. Consider it simply an efficient protection of the CPU in case of a major fault. 

SFC 46 is generally called by the operating system of the CPU in such cases, but it is also available to the user and can be used in the PLC program. I have never found a legitimate use for it in our own programs, a PLC shutting itself down without warning is not a result much appreciated by clients in our business. I have heard it be discussed as part of "booby traps" functions, to force payment from the client before a certain date for example, but we have never (thankfully) had to play such games with our clients. I hope this is not what you are thinking about, your reputation is much more important than such considerations.

Hope this helps,

Daniel Chartier

 Dear expert

Sorry for delay responding.

I'm just finding a reasonable solution for sttoping the plc except using SFC46.

Can you explain me what is the program in SFC46 that causes sttoping mode?

dchartier

Hello MJ90;

Do you mean can I explain the exact mechanisms by which SFC 46 places the CPU in Stop Mode?

I can't, and I doubt any simple Siemens programmer can give you insight in the internal functions of the Siemens OS.

The screenshot below, from the System and Standard Functions manual, presents the only information Siemens provides on the use of SFC 46. In other words: it works as shown, use it as given if you feel you need to.

https://support.industry.siemens.com/cs/ww/en/view/109751826

Hope this helps, (a bit),

Daniel Chartier

 Thanks so much dear Daniel.

So you mean there is no any extra information about the mechanisms of this system function block.