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S7-1200 set output.

Created by: Kamos at: 9/7/2014 8:16 PM (5 Replies)

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9/7/2014 8:16 PM	Rate (0)
Kamos Posts: 3 Rating: (0)	I am having a problem with setting a variable. When I use the set output with a relay output it works, but it doesn't seem to set a variable for the use in the system, it just acts as an ordinary assignament and when the input changes to false the output changes to false aswell, any idea what's wrong?
Kamos Posts: 3 Rating: (0)
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9/7/2014 8:36 PM	Rate (0)
William_B Posts: 5225 Rating: (1160)	Kamos I am having a problem with setting a variable. When I use the set output with a relay output it works, but it doesn't seem to set a variable for the use in the system, it just acts as an ordinary assignament and when the input changes to false the output changes to false aswell, any idea what's wrong? Please show us with a screen capture what the trouble is. Even better if you give us a sample program. w
William_B Posts: 5225 Rating: (1160)
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9/7/2014 10:29 PM	Rate (0)
Kamos Posts: 3 Rating: (0)	Thanks for replying, I have attached an image of the problem. The upper example works as it is supposed to, but the lower one acts as an ordinary assignament, while input=1 RokasRez=1, and as soon as the input becomes 0, the RokasRez variable becomes 0 aswell. I want it to stay as 1, as it is supposed to when I set it. Attachment Untitled-1.jpg (237 Downloads)
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9/7/2014 10:57 PM	Rate (0)
William_B Posts: 5225 Rating: (1160)	Thanks.. the picture does help. The #RokasRez is a local variable. It would be nice if I knew how its definition looks like. The variable is defined inside an FC / FB / OB code block and is defined as an input / temporary marker.. or some other variation To give it "memory" you can.. 1. use a memory bit Mx.y (much like Q0.0), or 2. create a STATIC variable inside an FB 3. create an IN/OUT inside an FC / FB 4. create a bit inside a global DB I am sure you already knew about (1). Point (3) is not helpful as it would still require another element (Q / M / DB bit) to give it memory. When you create and then use an FB, a memory block (DB = data block) is linked to this FB as soon as you call the FB in coding. The STATIC variables you create is kept as memory much as you do with Q0.0 - not only for bits but also other data types. Using the same idea you could also create an independant (global) DB. This creates variables for you that is stored to be called and reused by your coding. ---------------- Now these comments touches only the surface. I have burnt my fingers before to explain new members things that they already know -- new member does not mean beginner. If I am talking to a beginner (using Siemens), it will be most helpful to know your background. Our community can then more easily take it further. To get a frame of reference.. * Have you worked with PLCs before?.. which brand and model (even if Siemens)? * Which programming language do you know? (C++ / Java / VB /..) * Do you know about FC / FB / OB code blocks? I hope comments are helpful. Regards, w
William_B Posts: 5225 Rating: (1160)
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9/8/2014 6:24 PM	Rate (0)
Kamos Posts: 3 Rating: (0)	Thank you, I created a DB and declared the static variables there, everything works as it is supposed to now.
Kamos Posts: 3 Rating: (0)
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This contribution was helpful to 2 thankful Users 0_Einstein William_B

9/8/2014 6:39 PM	Rate (0)
William_B Posts: 5225 Rating: (1160)	Good news. Thanks for the feedback.
William_B Posts: 5225 Rating: (1160)
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