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indirect adressing with arrays

Created by: mracni at: 1/21/2011 2:29 PM (9 Replies)

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1/21/2011 2:29 PM	Rate (0)
mracni Regular Member Joined: 1/21/2011 Last visit: 5/23/2024 Posts: 13 Rating: (1)	Hi,I am a newbie in LAD & STL programing and I have problem understanding and writing code for this SCL code. [code] NEW := A OLD := ARR[PNT] ARR[PNT] := NEW [/code] this NEW and OLD are calculated in the rest of the code and are not a problem. I need to write this kind of code in STL or any other way that is not SCL. NEW & OLD are REAL defined in DB of FC in which is all of the code.ARR is array od REAL also defined in DB at adress DBD 24. PNT is UINT defined in DBW 228 and its value is initialized at 50 and later calculated in a logic that I can write in either STL or LAD. I need help in explaining how can I do this in STL,since I don't understand well indirect adressing. Thanks

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1/21/2011 3:12 PM	Rate (0)
jacek d Platinum Expert Joined: 9/23/2005 Last visit: 11/15/2024 Posts: 4793 Rating: (733)	Well, the simplest way is to write this in SCL. Then move the S7 project to the computer with Step7 without SCL installed. When you open there your block it will be pure STL.
	Regards, Jacek What is confusing you is the fact that you never see a number but always its digit representation. So you end up thinking that the number is the representation. - Andrej Bauer Any claims against me - based on whatever legal reason - resulting from the use of any code and/or ideas presented on this forum shall be excluded. #StayWithUkraine
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1/21/2011 3:22 PM	Rate (0)
Chilly_Garfield Posts: 316 Rating: (37)	Hi mracni, I agree to jacek d, but you need no STEP 7 without SCL. Compile the SCL source and copy the block who is created in a new project and then open the block, which you have copy in the new project. You will see the SCL code in STL. This will workby STEP 7.
Chilly_Garfield Posts: 316 Rating: (37)	Last edited by: Chilly_Garfield at: 1/21/2011 3:23 PM
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1/21/2011 3:36 PM	Rate (0)
mracni Regular Member Joined: 1/21/2011 Last visit: 5/23/2024 Posts: 13 Rating: (1)	haha,good idea,but problem is that my SCL code is not from siemens controler,so the syntax is not completely the same...

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1/21/2011 4:25 PM	Rate (0)
jacek d Platinum Expert Joined: 9/23/2005 Last visit: 11/15/2024 Posts: 4793 Rating: (733)	It's highly possible, that adjusting the SCL code to match Siemens SCL will be easier than learning STL. As low level languages usually require high level of skills.
	Regards, Jacek What is confusing you is the fact that you never see a number but always its digit representation. So you end up thinking that the number is the representation. - Andrej Bauer Any claims against me - based on whatever legal reason - resulting from the use of any code and/or ideas presented on this forum shall be excluded. #StayWithUkraine
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1/22/2011 11:52 AM	Rate (1)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 11/14/2024 Posts: 3027 Rating: (1057)	Hello mracni call me old fashioned but myadvise is: Take the plunge and do it directly in STL. Apart from reading up on indirect addressing (see link below), there's basically only threethings to bear in mind when doing so in STL: 1.) You ALWAYS work with absolute addresses (never symbolically) 2.) Any indirect access to DB's requires that you explicitly open the DB beforehand 3.) A "pointer" value in S7 is a 32 bit long value representing the Byte.Bit address(see also attached pic) that: a.) may additionally contain a memory area in the most significant Byte b.) ALWAYS points to a BIT address. What this means is the following: - Adding 1 to a pointer will point to the next Bit, adding 8 to a pointer will point to the next Byte, adding 16 to a pointer will point to the next Word etc. - Any typically available "Index" value that you have (e.g. an Integervalue in the range of 1 to 50 in your case) needs to receive a "SLD 3" to "convert" it to aByte.Bit "pointer" value (I'll do a "SLD 5" in the attached example which is a multiplication with 32 (bits) as we are dealing with REAL values). Anyway, attached is a pic with someSTL example code for your C logic and below is a link that "points" to someadditional info on this subject. Step 7- Indirect Addressing FAQ's I hope this helps to get you started andencourage you tohave a go at it in STL and come back shouldyou have more questions. Attachment Example STL code.jpg (1136 Downloads)
	Cheers fritz The advice and opinion given in this thread is that of the author and does not necessarily reflect the views of I S Systems Pty Limited. To find out how I S Systems can help you with your automation needs please visit www.issystems.com.au.
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2/1/2011 7:59 AM	Rate (0)
jacek d Platinum Expert Joined: 9/23/2005 Last visit: 11/15/2024 Posts: 4793 Rating: (733)	fritz call me old fashioned but myadvise is: Take the plunge and do it directly in STL I don't agree. Useing STL is not old fashioned. But it's simplyeasier to master SCL than STL. Why? BecauseSCL is"higher" level language .
	Regards, Jacek What is confusing you is the fact that you never see a number but always its digit representation. So you end up thinking that the number is the representation. - Andrej Bauer Any claims against me - based on whatever legal reason - resulting from the use of any code and/or ideas presented on this forum shall be excluded. #StayWithUkraine
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3/18/2019 11:03 AM	Rate (0)
DRG158A Regular Member Joined: 6/7/2015 Last visit: 5/20/2024 Posts: 29 Rating: (0)	Hi, I used this code and it works well...BUT if you use an integer value of 1025 when making the pointer and the so points at the address of REAL DBX 4096.0 , it causes the PLC to fault . This is in both a 315 and a 317...why would that be ?? Cheers !

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3/19/2019 12:33 AM	Rate (0)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 11/14/2024 Posts: 3027 Rating: (1057)	DRG158A .BUT if you use an integer value of 1025 when making the pointer and the so points at the address of REAL DBX 4096.0 , it causes the PLC to fault . ...why would that be ?? It's because Siemens decided to make "+AR1" a signed 16 bit Integer addition which limits it to a positive pointer value addition of 4095.7 (and I presume you use the +AR1 instruction). Using a pointer value of 4096.0 with +AR1 actually decreases AR1 by P#4096.0 which I fear is the cause for your PLC stop. Solution is simple, do a "+D" DINT based pointer math addition beforehand followed by "LAR1".
	Last edited by: fritz at: 3/19/2019 4:33:35 AM Cheers fritz The advice and opinion given in this thread is that of the author and does not necessarily reflect the views of I S Systems Pty Limited. To find out how I S Systems can help you with your automation needs please visit www.issystems.com.au.
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3/27/2019 1:11 AM	Rate (0)
DRG158A Regular Member Joined: 6/7/2015 Last visit: 5/20/2024 Posts: 29 Rating: (0)	Thanks Fritz ! I got it sorted out. Cheers Steve

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