S5 operation JU +1

iPegg · Mar 7, 2014

I have a question that I think will be simple to answer, but I could not find a solution from looking through the manuals. There is an instruction:

JU +1

in an S5 program that I am trying to convert to S7. What does this mean, and how do I implement it in S7? My guess was that it simply meant go to the next line, but then what would be its purpose?

Thanks in advance for your help

JesperMP · Mar 7, 2014

Maybe there is a label called "+1" ?

krk · Mar 7, 2014

Are you sure it's JU and not JUR where you specify an absolute jump distance?

iPegg · Mar 7, 2014

It may be JUR, I'd have to go back and check. But would it have any effect other than going on to the next instruction?

Edit:

I did get it wrong, the command was JUR. So does this simply mean a jump to the next instruction?

KalleOlsen · Mar 7, 2014

JesperMP said:
Maybe there is a label called "+1" ?

No, the labels must start with "=".

Kalle

seppoalanen · Mar 7, 2014

There must be something before that jump command.
It gould be as "select case" command.

danatomega · Mar 7, 2014

Yes, JUR is a JUmp Relative so +1 indicates the next instruction. Maybe they used it as a placeholder or they were jumping further and decided not to anymore and made it +1?

L D[AR2P#0.0] · Mar 7, 2014

Which S5 CPU is the code from ? - As an example, here's a link to a 928B CPU which describes the JUR instruction.

http://support.automation.siemens.com/WW/view/en/19397726

The possibility of a case statement has been mentioned (this uses the DO command) but the JUR instruction is not allowed with the DO command (for the 928B at least).

Unlikely, but possible, is that the the program is self modifying and the relative jump changes at run time to implement the case statement.

Another unlikely but possible scenario is that the code is actually data hidden in the function block - the section of code you are seeing is never meant to be executed.

iPegg · Mar 10, 2014

L D[AR2 said:
Which S5 CPU is the code from ? - As an example, here's a link to a 928B CPU which describes the JUR instruction.

http://support.automation.siemens.com/WW/view/en/19397726

The possibility of a case statement has been mentioned (this uses the DO command) but the JUR instruction is not allowed with the DO command (for the 928B at least).

Unlikely, but possible, is that the the program is self modifying and the relative jump changes at run time to implement the case statement.

Another unlikely but possible scenario is that the code is actually data hidden in the function block - the section of code you are seeing is never meant to be executed.

Thank you! I'll take a look at the code to see if its doing anything funky like that. I really hope it's not, because that will be a real pain in the *** to duplicate in S7.

S5 operation JU +1

iPegg

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JesperMP

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krk

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iPegg

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KalleOlsen

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seppoalanen

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danatomega

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L D[AR2P#0.0]

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iPegg

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