S7 Status Word Buildup

Andrew Evenson · Mar 31, 2005

Ladies & Gentlemen,

I hope someone can maybe lead me in the right direction..

It is my first time dabbering with a Siemens S7-300. I decicded to duplicate some code we use on our automation platform, to play around with because I know how it works. The automation platform is not Siemens. It is from a company called Alstom. In the Alstom platform, you can combine bit and word logic in the same rung. This is what I am trying to achieve in the Siemens.

Alstom Example:

Note : The left hand rail cannot be considered a "power" rung or "1" , it has a value if -1 or Hex FFFF.

  

 

|----||---<AND>----------------------------------(OUT)------|

|   a0.0   @1   |                    |            g10

|               |                    |

|----||---<AND>-|-<OR>---||--<AND>---|

    a0.1   @2    @FFFF  a0.2  @20

I should explain some things about the code.

The "a" and "g" address are integer values, not different than a "B" address in Allen Bradley. The "@" sysbol denotes a hex value.**This last stentence is key*** The <AND> is no different than what it implies. The <OUT> instruction is like the "Transfer" function in Siemens.

The above code works like this, you are basically creating a bit pattern within "g10" by setting bits withing g10 based on the conditions of the a0 bits. This allows you to buildup the word to represent different conditions or what ever you want. We use this for our HMI's to represnt a status for a device, instead of sending induvidul bits to the HMI.

If no "a0" bits are set, g10 = 0
If a0.0 is set, g10 = 2
If a0.1 is set, g10 = 4
If a0.0 and a0.1 are set, g10 = 6
If a0.2 is set, g10 = 32
If all bits are set, g10 = 38

I can figure out how to do this in Siemens, may take quite a bit of code, just trying to see if they have a "canned" instruction to do this?? I've looked, but cant seem to find anything.

Please ask if my explination is confusing...

Any help would be appriciated..

Thank you,

Andrew

Terry Woods · Mar 31, 2005



    +-----------+                 +----------------+  ALWAYS

    |   "AND"   |   Result1   0   |    "MOVE"      |   OFF

----+ SOURCE"A" +----------|=|----+    "0" to      +---| |---+----( DUMMY )

    | Mask1(111)|                 | DESTINATION"G" |         |

    |  Result1  |                 +----------------+         |

    +-----------+                                            |

                                                             |

                                                             |

    +-----------+                 +----------------+  ALWAYS |

    |   "AND"   |   Result2   0   |     "ADD"      |   OFF   |

----+ SOURCE"A" +----------|>|----+ DESTINATION"G" +---| |---+

    | Mask2(001)|                 |      +2        |         |

    |  Result2  |                 |  ------------  |         |

    +-----------+                 | DESTINATION"G" |         |

                                  +----------------+         |

                                                             |

                                                             |

    +-----------+                 +----------------+  ALWAYS |

    |   "AND"   |   Result3   0   |     "ADD"      |   OFF   |

----+ SOURCE"A" +----------|>|----+ DESTINATION"G" +---| |---+

    | Mask3(010)|                 |      +4        |         |

    |  Result3  |                 |  ------------  |         |

    +-----------+                 | DESTINATION"G" |         |

                                  +----------------+         |

                                                             |

                                                             |

    +-----------+                 +----------------+  ALWAYS |

    |   "AND"   |   Result4   0   |     "ADD"      |   OFF   |

----+ SOURCE"A" +----------|>|----+ DESTINATION"G" +---| |---+

    | Mask4(100)|                 |     +32        |

    |  Result4  |                 |  ------------  |

    +-----------+                 | DESTINATION"G" |

                                  +----------------+

The ALWAYS OFF bit ensures that the next branch is always evaluated before bailing out of the rung.

If the Destination "G" is a Byte, then the Masks are bytes...

Mask1 = VB(X+0) = 0000 0000
Mask2 = VB(X+1) = 0000 0001
Mask3 = VB(X+2) = 0000 0010
Mask4 = VB(X+3) = 0000 0100

I used "VB(X+0)" just to make them line up pretty.

The same scheme can be used for any weird-weighting that you might put on the particular bits.

SimonGoldsworthy · Apr 1, 2005

G needs to be initialised to 0 before this logic is performed.

SimonGoldsworthy · Apr 1, 2005

Andrew - where are the status bits going to exist after you have built them up ? If they are in a DB why not create the DB as a set of bits and then control the bits individually with simple logic. This will be a lot clearer and simpler.

Andrew Evenson · Apr 1, 2005

thank you..

Gentlemen,

Thank-you for your reponses. Simon,that is what is essentially happening in my code. I'm just not too versed in Siemens yet. I was acctually thinking about that ways of doing it after I posted. I was actually trying to do this within a Function Call. I was able to define a word, say called "status", but didnt know how to manipulate the words induvidual bits. Is there a way?? OR does it can it only be done through a DB?? Im basically trying to send a word out of the FC that represents different conditions, so it can be interogated somewhere.All I am doing is playing around and learning how to pass parameters in and out of a FC and came across a stumbling block withing the FC.

Again, thank you both for your effort and time.

Thank you,

Andrew

SimonGoldsworthy · Apr 1, 2005

Andrew, the question to be answered is:

Is the word used to code a status 0,1,2 etc. correspond to 65536 different status messages, or,
does each bit of the word correspond to 16 separate status messages.

If the former, use a function to pass out a word, if the latter, output 16 bools which you can then parameterize to bits in a db.

The db bits method (recommended) will allow you to cross-ref and track down the status reporting. Setting bits in a word in the accumulator and then outputing the word into a db will be very difficult to track down later.

Terry Woods · Apr 1, 2005

"G needs to be initialised to 0 before this logic is performed."

Indeed it does... I didn't sleep very well thinking about this... but I was too tired to get up and fix it.

In the first branch of the rung, instead of testing for zero, simply load zero into G. Then proceed to evaluate the bits with the remaining branches.

S7 Status Word Buildup

Andrew Evenson

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Terry Woods

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SimonGoldsworthy

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SimonGoldsworthy

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Andrew Evenson

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SimonGoldsworthy

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Terry Woods

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