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Step7 bugs

Created by: how come at: 6/8/2009 9:16 AM (11 Replies)

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6/8/2009 9:16 AM	Rate (0)
how come Posts: 382 Rating: (47)	Dear all, I encountered something quite strange which I couldn't figure out why. 1] From my attached figure 1, I got some "rubbish" values from the local variable at the 2nd rung whereas my 1st rung is zero in values. 2] From my attached figure 1, if I used MDxxx, the values are the same for both rungs. I am not sure why using the local variable will give some "rubbish" values. Anyone one encounter this before? Thanks! with regards, how come? Attachment Step7 Bugs.zip (351 Downloads)
how come Posts: 382 Rating: (47)
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6/8/2009 10:00 AM	Rate (1)
Sydney Gold Member Joined: 1/4/2008 Last visit: 9/26/2024 Posts: 703 Rating: (96)	Hello, please don't use theterm "Step7 bugs" before you know what is the problem, because this is your fault . The TEMP memory have to be ALWAYSinitialized before using! You write to the local variables just when the edge of signal comes, but when it doesn't in the TEMP memory you have anything from some another block called before which uses the same memory area. Look at the manual for the Step7 programming here: http://support.automation.siemens.com/WW/view/en/18652056 Regards Sydney
	Last edited by: Sydney at: 6/8/2009 10:05 AM
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6/8/2009 2:08 PM	Rate (0)
Navnag Platinum Member Joined: 11/21/2007 Last visit: 9/25/2024 Posts: 2325 Rating: (308)	Dear how come ? For such data you need to use a Data Block area or Flag ( M area ) and not Temp Variables. Also Pl keep track of Variable Type definition IN / OUT / INOUT depending on the usage type Regards Navnag
	There is no such thing as the last bug in a program There are no stubborn bugs, There are only stubborn Debuggers.
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6/8/2009 8:02 PM	Rate (0)
Ayman Elotaify Platinum Expert Joined: 5/28/2008 Last visit: 11/6/2024 Posts: 4516 Rating: (839)	Hello How come?, I have noticed very important thing in your first file. You have defined the local data DD_Value 3_1 & DD_Value 3_2, both is real value. You have defined DB10.DBD24 as DINT or DWord; Iam not sure. It should be real. Because you are moving the content of this value into the local variable. So, open DB10 and go to the type of DB10.DBD24 and make it real. save it! re-download it to your CPU and monitor and let us know the results. With best regards,
	Ayman Elotaify
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6/8/2009 8:57 PM	Rate (0)
Sydney Gold Member Joined: 1/4/2008 Last visit: 9/26/2024 Posts: 703 Rating: (96)	Hmm, I tried to look as much as I can but still can't findthe declaration ofthat DB variable in the picture, how do you know it isn't REAL? Telepathy?

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6/9/2009 6:42 AM	Rate (0)
how come Posts: 382 Rating: (47)	Dear Sydney, Navng & Ayman Elotaify, Thank you very much forall your inputs.OOps sorry,don't mean to say siemens step7 problem. Maybe I should use "program problem encountered" By the way, Ayman Elotaify, My DB10 data type are all real. So don't think that could lead to the problem i faced. But still appreciate your input. Anymore idea that you can think off? Thanks! with regards, how come?
how come Posts: 382 Rating: (47)
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6/9/2009 7:39 AM	Rate (0)
Ayman Elotaify Platinum Expert Joined: 5/28/2008 Last visit: 11/6/2024 Posts: 4516 Rating: (839)	Dear How come? Are you sure that bothe variables "Value3_1" & "Value3_2" are not used in any other network in this function? as may be some networks else wrote these values in. Regards,
	Ayman Elotaify
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6/9/2009 12:16 PM	Rate (0)
H-H Platinum Member Joined: 7/2/2008 Last visit: 9/30/2024 Posts: 928 Rating: (309)	Hello How Come? It's quite straight. As Sydney had already said Temp variables should always be initialized before use. The point is TEMP variables are not appropriate solution for what you are trying to do. TEMP variables are used locally in the FB or FC you are calling and they can't retain their values until the next time this particular FC is called because any call for any otherFC or FBbefore or after this FC might change values of TEMP variables (Local data). You can use TEMP variables (After initialization) for data that you need instantaneously (TEMPorarily). For example if you have a long mathematical equation and you don't need to keep the middle terms and numbers and just need the final outcome of that equation. In this case you'd better use TEMP variables as registers for middle terms that you don't need after executing this function. But in your case, you need to save ANALOG_OUTPUT_DIGITAL_DISPLAY_3 for certain time for some purpose. You can't use TEMP variables because they will not retain values until you need them again. Even intializing TEMP variables will not help. You can useMarkers' areaas in second picture or datablcoks for more well organized program. Best regards. H-H

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This contribution was helpful to 1 thankful Users Sydney

6/10/2009 5:35 AM	Rate (0)
how come Posts: 382 Rating: (47)	Hi, Ayman Elotaify, I have did a cross reference check and very sure that the variables are not use anywhere else. H-H, what is Marker's area that you have mention. Sorry I couldn't get it. Possible to explain a little more to me? Thanks. ya, one more thing is about the initializing of the TEMP. How I can go about initializing it? or I must move zero to all local variables at the beginning of the rung in order to initialize them? Thanks and appreciate all of your ideas and inputs with regards, how come?
how come Posts: 382 Rating: (47)
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6/10/2009 10:35 AM	Rate (1)
Sydney Gold Member Joined: 1/4/2008 Last visit: 9/26/2024 Posts: 703 Rating: (96)	Hello, forget searching if used, the problem is that you can't use TEMP area for this. Initialization means that you have to assign any value before reading. You don't need to put zero there if you use it as mentioned for storing temporary results because you transfer there a value which you read later. The same principle is for the bit acces, you should use the output coil (assign instruction) before reading (If you'd like to use SR you should first assign the init state).Marker is pretty old term from the S5 PLCs but still often used also in S7 PLCs. The memory area, in english called rather flags is addressed asM*, you've already used it in your second case. For your application I would suggest to use the datablock. Regards Sydney

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This contribution was helpful to 1 thankful Users H-H

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