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Local memory direct access

Created by: dendhondt at: 1/17/2013 12:29 PM (10 Replies)

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1/17/2013 12:29 PM	Rate (0)
dendhondt Bronze Member Joined: 8/5/2009 Last visit: 7/4/2022 Posts: 156 Rating: (7)	Hi, In an Step 7 project a loaded a word from a db into the temp memory This tempmemory was a UDT of 16 bits OPN DB1 L DBW[#Point] T LW0 In TIA portal i can not use LW0 How can i make this work? I saw in a getting started project i can use the AT function for a Date_And_Time format, is there something similar for my problem?

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1/17/2013 1:49 PM	Rate (0)
Darius Platinum Expert Joined: 9/28/2005 Last visit: 12/10/2024 Posts: 2957 Rating: (243)	Use '%' sign before LW in TIA. It's like T %LW0 and it will work as you want.
	Best regards, Darius
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1/18/2013 12:30 PM	Rate (0)
dendhondt Bronze Member Joined: 8/5/2009 Last visit: 7/4/2022 Posts: 156 Rating: (7)	yes it works but i get a warning message " Access to %LW0 with ambiguous adress" and the code line stays yellow

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1/18/2013 12:52 PM	Rate (0)
Marko Bursic Platinum Member Joined: 9/8/2009 Last visit: 7/17/2023 Posts: 1410 Rating: (153)	Why don't you give a symbolic name to your temporary variable. The local stack is self modifiing, so its not a good idea to transfer data directly on address of your choice, like LW0. If you name one temp variable and transfer to it, compiler will self organize on whichlocal address will store it, you can seethis address in editor. If you use ladder programing, the compiler willstore intermediate results in local stack, they will be hidden and not visible in editor, except if change the view into STL you will see a lot of L x.y bits L words that you didn't program, so direct transfer to local stack is not recomandable unless you exactly know what you're doing.

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1/18/2013 12:55 PM	Rate (0)
Darius Platinum Expert Joined: 9/28/2005 Last visit: 12/10/2024 Posts: 2957 Rating: (243)	dendhondt yes it works but i get a warning message " Access to %LW0 with ambiguous adress" and the code line stays yellow Once I have opened support request case on this error. Siemens developement team meade lots of internal discussions, but they decided to leave it as is because new philosophy tells that it's not good idea to use address without symbol. Just ignore this message as it do not influence program flow.
	Best regards, Darius
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1/18/2013 12:59 PM	Rate (0)
Darius Platinum Expert Joined: 9/28/2005 Last visit: 12/10/2024 Posts: 2957 Rating: (243)	Marko Bursic Why don't you give a symbolic name to your temporary variable. The local stack is self modifiing, so its not a good idea to transfer data directly on address of your choice, like LW0. Sometimes symbolic addressing doesn't help. Suppose you have input or temporary variable of type POINTER or ANY. You need to access separate bits of this variable in order to construct required pointer to required memory area. In that case you have no chance to use symbolic access, only way is %LBxx.
	Best regards, Darius
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1/18/2013 1:32 PM	Rate (0)
Marko Bursic Platinum Member Joined: 9/8/2009 Last visit: 7/17/2023 Posts: 1410 Rating: (153)	I know that in very rare situations is useful to go wit direct access on local stack. Marko Bursic , so direct transfer to local stack is not recomandable unless you exactly know what you're doing.

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1/18/2013 10:24 PM	Rate (0)
dendhondt Bronze Member Joined: 8/5/2009 Last visit: 7/4/2022 Posts: 156 Rating: (7)	I want to use the symbolik name but i don't know how? My temporary variable has a symbolik name STAT, the data type is an UDT the UDT contains 16 bools When i do: OPN DB 1 L DBW[#Point] T #STAT This doesn't work, it expects the #STAT.VariableName But i want to Transfer a word to the entire word not only one bit Attachment ProblemSymbolik.jpg (520 Downloads)
	Last edited by: dendhondt at: 1/19/2013 12:16 AM
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1/19/2013 12:16 AM	Rate (0)
Marko Bursic Platinum Member Joined: 9/8/2009 Last visit: 7/17/2023 Posts: 1410 Rating: (153)	Rule No1: Don't give a symbolic names like STAT,TEMP,BOOL,INT,.... If this is a part of an old program then instruction T LW0 shoud work, because STATstarts on address L0.0, everything is OK. Delete T #STAT, because you can't transfer a word into UDT variable. You can also use AT statement. Or you can use pointer to your variable named STAT: L P##STAT LAR1 OPN "DB,..blabla L DBW....blabla T LW[AR1,P#0.0] Anyway shouldn't be a problem to compile that program (of course delete T #STAT statement)

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1/19/2013 4:33 PM	Rate (0)
dendhondt Bronze Member Joined: 8/5/2009 Last visit: 7/4/2022 Posts: 156 Rating: (7)	i want to use the AT command, but with S7-300 its only possible in SCL I will use this L P##STAT LAR1 OPN "DB,..blabla L DBW....blabla T LW[AR1,P#0.0]

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