S7 to SIMOTION data conversion problem

Jerry Holzer

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• Apr 6, 2006

• #1

I am trying to devise a way to get floating point data from a S7 processor to a SIMOTION processor over a fieldbus link. When I send a float over to the SIMOTION, it stores the data in IEEE 754 format over four consecutive bytes. I can't figure out how to get that data into a native floating point variable within Simotion. Any ideas?

 

Peter Nachtwey

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• Apr 6, 2006

• #2

Jerry Holzer said:

I can't figure out how to get that data into a native floating point variable within Simotion. Any ideas?

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It would help if we knew the native floating point format with the Simmotion. Doesn't the Simotion also use IEEE floating point?

If Siemens were smart they would use the same floating point format in their motion controllers as the PLC uses. They must. It would be brain dead not to. The TI DSP we use on our Profibus DP enabled motion controller uses its own floating point format and isn't compatible with anything. However, we anticipated problems such as yours so we always convert to and from IEEE format when communicating with external devices. The user isn't aware of the conversion. It is the only thing that makes sense. The cost of doing the conversion yourself should be added to the cost of the motion controller when making a buying decision.

 

Jerry Holzer

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• Apr 6, 2006

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Peter Nachtwey said:

If Siemens were smart they would use the same floating point format in their motion controllers as the PLC uses.

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From what I can tell so far, everything Siemens does is baffling. Why I have to build something as basic as this out of rocks and garbage is beyond me! Why Siemens has the market share it has outside the USA is even more baffling. I'll have to back off on my Rockwell bashing from now on

The problem is the data is stuck in a byte-level data array. There is native floating point variable support. What I can't work out is how to get four consecutive bytes containing the 2's compliment variable data into a native variable.

 

Peter Nachtwey

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• Apr 6, 2006

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Can't you change the format of how the data is displayed? You probably have the right data but can't see it because it is in byte format instead of floating point format.

 

Jerry Holzer

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• Apr 7, 2006

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No, you just can't get there from here. The data isn't in the right PLACE. It's stuck in an array that came in from a UDP message over ethernet. We basically have to write a routine to convert four consecutive data elements from the binary representation of a floating point number to a native floating point number. I think we found a workable method and will post our solution if it works out.

 

jacekd

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• Apr 7, 2006

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How about BigByteArray_To_AnyType function ?
However kernel 2.1 or newer is required.

 

Jerry Holzer

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• Apr 7, 2006

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I wasn't aware Siemens used Linux for their processors If only.

 

jacekd

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• Apr 7, 2006

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They also aren't aware they did .

 

Jerry Holzer

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• Apr 7, 2006

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Are you proposing that the SIMOTION processor is based on linux?

 

jacekd

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• Apr 7, 2006

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Just a joke. I have no idea what they used.
In my post "kernel" means "Simotion kernel" - to make things clear.

 

Peter Nachtwey

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• Apr 7, 2006

• #11

Ouch

Jerry Holzer said:

We basically have to write a routine to convert four consecutive data elements from the binary representation of a floating point number to a native floating point number.

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Or you can buy equipment that doesn't reqire the extra work. Either way it is your time or your money. There are motion controllers, PLCs and HMIs that work together very cleanly and simply. This should be simple. These kinds of thing are done all the time.

I can see why your avitar looks frazzled.

 

jacekd

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• Apr 9, 2006

• #12

Peter Nachtwey said:

Or you can buy equipment that doesn't reqire the extra work.

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Simotion does not require this extra work. Kernel 2.1 is availible since 2002.
Real Jerry's problem is that he didn't RTMF.

 

Jerry Holzer

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• Apr 10, 2006

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I would RTFM if I could understand German. Believe me, Siemens is NOT my idea. If I had my choice, it would be a combination of Rockwell PLC and Bosch/Rexroth (Indramat) motion control. Certain market sectors in some parts of the world require Siemens for some unknown reason. Conservation of European angst perhaps

 

jacekd

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• Apr 10, 2006

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Funny thing. I don't speak German at all. (OK - maybe few nice words but not to be presented in public. ) And Siemens usually doesn't take care of my native language. So how did I manage to RTFM ? Hmm... Let's think... Bingo - it must have been in English then. All you need to do is to put some effort and find it.