S7, Indirect Jumping Possible ??

pethoek · Sep 11, 2010

I wonder if there is a way of doing indirect jumping in S7.

This is what i would like to do....

Code:

LAR1 P##Ptr // Pointer addr
L W#16#1018 // FC - Type
L W [AR1,P#0.0]
L W#16#0
T W [AR1,P#2.0] // Word 2 = 0
T W [AR1,P#4.0] // Word 4 = 0
T W [AR1,P#6.0] // Word 6 = 0
L W#16#2 // FC 2
T W [AR1,P#8.0] // FC Number

Now i was hoping i could do something like

CALL Ptr, instead of CALL FC 2

And by changing the number for FC in the pointer, be able to call for different FC's.

I can ofcource use some kind of jump table
if x=1 then call FC 2
if x=2 then call FC 3

But i think it would be a nice way of calling different FC's just by passing a FC-number to some FC and the call for that FC was made.

Is there a way of doing this in S7.

Best Regards
Pethoek

pethoek · Sep 11, 2010

Well at second thought, different FC's may have different parameters passed so it is perhaps not possible.

pethoek · Sep 11, 2010

Guess a simple solution to my problem would be something like...

Code:

L #ID
 
L 2
==I 
CALL FC 2
 
TAK 
L 3
==I 
CALL FC 3
 
TAK 
L 4
==I 
CALL FC 4
 
"
"
"

L D[AR2P#0.0] · Sep 11, 2010

... with some jumps around the calls (JCN skp2) and a jump to the end of the table after each call (accu will have changed) of course!

Peter Nachtwey · Sep 11, 2010

See the JL instruction

It allows one to make jump tables and is much more efficient than your code.

There isn't a true pointer indirect jump in S7 and it would be dangerous in the hands of the average PLC programmer.

L D[AR2P#0.0] · Sep 11, 2010

Here's how to call an FC indirectly. No parameters can be passed but if the FC does have parameters they will be read as if they are parameters from the code that is after the UC

L D[AR2P#0.0] · Sep 11, 2010

As mentioned by Peter, the JL instruction is useful for case statements, e.g.

pethoek · Sep 11, 2010

hmmm...

/edit...

Code:

      L     #ID
      L     2
      ==I   
      CC    FC     2
 
      TAK   
      L     3
      ==I   
      CC    FC     3

pethoek · Sep 11, 2010

Ok thanks.. i have no an idéa of how to proceed..

L D[AR2P#0.0] · Sep 11, 2010

Sorry to mislead you but this is not a practical method. I am pointing out that if you called an FC using the UC FC method and the FC had parameters, the FC would attempt to access the parameters using the data present in the calling block immediately after the call - this would be the S7 opcodes !!!

bara_hence · Sep 11, 2010

Why not just use the jl method and have the panel load a value in a int register representing the button pressed..

STL??? · Sep 11, 2010

I would also add limits here incase a FC is selected and doesnt exist inside your program.

Obviously the JL method would handle this.

Peter Nachtwey · Sep 11, 2010

You can pass parameters in a register or..

you can pass a pointer to the parameters in a register. These parameters can't be accessed as input or output parameters though. Essentially this is what the S7 code does when it calls a FB. AR2 is loaded with a pointer to the DB. This makes L D [AR2,P#0.0] first method more usable.

I really wish I could do this
L D [AR2,P#VAR1]
L D [AR2,P#VAR2]
+
T D [Ar2,P#VAR3]

S7, Indirect Jumping Possible ??

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