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SEL (Select) instruction doesn't support boolean variables

Created by: chriswu at: 2/8/2013 1:13 AM (5 Replies)

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2/8/2013 1:13 AM	Rate (0)
chriswu Posts: 8 Rating: (1)	Can somebody enlighten me on this very simple task? I tried to use the SEL instruction in FBD. The problem is both the IN0 and IN1 wouldn't take boolean variables. All I want to accomplish is to move either IN0(bool) or IN1(bool) to the output(bool) depending on the status of the switch(bool). There must be an easy way to do this. I tried MOVE but it doesn't take boolean either. On another note, I'm unable to use a boolean constant. Does Siemens hate boolean?
chriswu Posts: 8 Rating: (1)
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2/8/2013 12:07 PM	Rate (0)
Marcjan Platinum Member Joined: 4/22/2010 Last visit: 12/15/2022 Posts: 5697 Rating: (709)	Hello, Siemens has a lot of bit logic to solve your boolean puzzle, be creative. The SEL function is to move Word at input to output, you can use it to move your bit but only with 16 at a time. Regards, Marcjan
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2/9/2013 12:43 AM	Rate (0)
chriswu Posts: 8 Rating: (1)	Thank you for answering my question first of all. I understand I could use two "&" instructions and one ">=1" instruction to select a boolean. What I don't understand is why it's not an instruction pre-defined by Siemens. I was thinking someone might know an instruction that does boolean selection.
chriswu Posts: 8 Rating: (1)
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2/9/2013 6:03 PM	Rate (0)
hdhosseini Diamond Expert Joined: 1/28/2009 Last visit: 12/8/2023 Posts: 6827 Rating: (1351)	chriswu Thank you for answering my question first of all. I understand I could use two "&" instructions and one ">=1" instruction to select a boolean. What I don't understand is why it's not an instruction pre-defined by Siemens. I was thinking someone might know an instruction that does boolean selection. Hello , There are some standards should be followed by PLC manufacturers like SIEMENS.For Programming languages you can check Part 3 of IEC 61131.These are the links : http://en.wikipedia.org/wiki/IEC_61131-3 Best regards Hamid Hosseini
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2/9/2013 7:40 PM	Rate (0)
chriswu Posts: 8 Rating: (1)	HiHamid, Did you mean Siemens didn't offer this instruction because the IEC standards either didn't ask for it or didn't allow it? At least some of Siemens' competitors, such as Modicon's Unity Pro XL, have a built-in boolean selection instruction.
chriswu Posts: 8 Rating: (1)	Last edited by: chriswu at: 2/9/2013 7:41 PM Last edited by: chriswu at: 2/9/2013 7:40 PM
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2/9/2013 8:34 PM	Rate (0)
hdhosseini Diamond Expert Joined: 1/28/2009 Last visit: 12/8/2023 Posts: 6827 Rating: (1351)	chriswu HiHamid, Did you mean Siemens didn't offer this instruction because the IEC standards either didn't ask for it or didn't allow it? At least some of Siemens' competitors, such as Modicon's Unity Pro XL, have a built-in boolean selection instruction. Hello , This is not a place to talk about different design strategies in different manufacturers.But, here I just analyze why having a binary selector is worthless. I hope you are using FC36(SEL) in TIA for S7300 and S7400. This is categorized as digital functions and data types such as BYTE,WORD,DWORD,... are selected by binary input "G". Please, note to implement this structure in STL,LAD,FBD you need a complex conditional jump structures to select the output based on controlling signal. But for a binary selector like that, you can do it by 2 nets of codes here: [code]AN M0.0 // as G, if false A I0.0 = Q0.0 A M0.0 // as G, if true A I0.1 = Q0.0[/code] If you have more options i.e control signal is an INT,you can do it with comparators(Boolean outputs) and simple basic binary logic. This what we can guess without accessing design team. Best regards Hamid Hosseini
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