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Using pointers in STL

Created by: Raffy at: 4/4/2013 5:34 AM (9 Replies)

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4/4/2013 5:34 AM	Rate (0)
Raffy Posts: 209 Rating: (2)	Hi guys... I would just like to ask what does this program do and its functions... I'm still a beginner at using stl and I can't decipher the meaning of some codes... I uploaded a sample program for pointers... could somebody explain to me how does this stl program work?? thank guys, Raffy Attachment pointers.JPG (2993 Downloads)
Raffy Posts: 209 Rating: (2)
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4/4/2013 7:20 AM	Rate (1)
KayBee Posts: 241 Rating: (7)	Hi, Raffy, I hope this will clear your doubt. Please see the attachement for your answer. Enjoy Attachment pointers[1].jpg (3167 Downloads)
KayBee Posts: 241 Rating: (7)
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This contribution was helpful to 1 thankful Users Raffy

4/4/2013 8:14 AM	Rate (0)
Raffy Posts: 209 Rating: (2)	Thanks Kaybee... But I don't understand how the program convert L#12 to pointer address.... I guess I don't really understand the syntax of pointers and how it works.... Ithought SLD 3 is a shift left function which shifts the bits 3 times to the left.....so if I change it to SLD 4 would it change the function of the program?? But many thanks I really understand most of the program now..
Raffy Posts: 209 Rating: (2)
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4/4/2013 11:29 AM	Rate (0)
KayBee Posts: 241 Rating: (7)	Raffy, You are right. the instruction SLD 4 would change the function of the program. By using SLD 3 instruction, 32bit double integer value is shifted 3 digit left to occupy last 3-bit information of bit addressing. Truely speaking if your integer value is 12 then SLD would convert that to addressing format that is 12.0 where 12 is byte number and 0 is bit number. See attachement for pointer structure. This "Any" type 10byte pointer of which last 4-bytes are addressing-pointer (byte 6-9) you need to see. hope you are now clear. Attachment s7 pointer 1.jpg (2184 Downloads)
KayBee Posts: 241 Rating: (7)	Last edited by: KayBee at: 4/4/2013 11:34 AM
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This contribution was helpful to 1 thankful Users Raffy

4/4/2013 11:44 AM	Rate (0)
jacek d Platinum Expert Joined: 9/23/2005 Last visit: 12/19/2025 Posts: 5147 Rating: (772)	Pls go to online help of Step7 Manager and find in the index "Pointer">"Format of the parameter type POINTER". Format of pointers in STL is same excluding first 2 bytes. Basically converting from byte address (ex. byte 12) is done by SLD 3 instruction. Howeverwhen accessing word/dword arrays it may be more usefull to use SLD 4/SLD 5.
	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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This contribution was helpful to 2 thankful Users KayBee Raffy

4/4/2013 12:51 PM	Rate (0)
KayBee Posts: 241 Rating: (7)	jack d, do you have some example using SLD 4, or SLD 5 to access word or dword in STL for S7 plc. I would very thankful to you. Thanks
KayBee Posts: 241 Rating: (7)
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This contribution was helpful to 1 thankful Users Raffy

4/4/2013 1:50 PM	Rate (2)
jacek d Platinum Expert Joined: 9/23/2005 Last visit: 12/19/2025 Posts: 5147 Rating: (772)	Let's suppose you want to access array of ints/reals using index. And let's presume that correct DB is opened and starting address of the array loaded to AR1. [code]L #index SLD 4 // in case of ints, put here 5 in case of reals (or dints) +AR1 L W[AR1,p#0.0] //in case of reals use D instead of W[/code] How it works ? Shifting binary number one position to the left is equal to multiplying it by 2. In case of array of ints indices and corresponding addresses looks like below: idx addr 0 0 1 2 2 4 ... So we take index, shift it by 1 to multiply it by 2 and shiftresult by 3 to obtain correct address format. 1+3 = 4 ;) Similar operation in case of reals, but here we have to shift by 2 because it must be multiplied by 4.
	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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This contribution was helpful to 3 thankful Users Karls1 chikhim Raffy

4/8/2013 2:39 AM	Rate (0)
Raffy Posts: 209 Rating: (2)	Hello Guys, Thanks for the help..It was really a big help for me.... Now it easier for me to access or transfer data through pointers... Best regards, Raffy
Raffy Posts: 209 Rating: (2)
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This contribution was helpful to 1 thankful Users Sherryooo

8/24/2016 12:30 AM	Rate (0)
Min_Moderator Posts: 4758 Rating: (122)	New question published by icaroiko2 is split to a separate thread with the subject Pointer and array in STEP 7. Best regards Min_Moderator
Min_Moderator Posts: 4758 Rating: (122)
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This contribution was helpful to 1 thankful Users DIEsel27031992

8/26/2016 4:30 PM	Rate (0)
Sapher_Jalt Posts: 17 Rating: (1)	Wow... but... Why L#12? Why not L#14 or L#18? Where did we take this value? How we go from pointer to local data? Can u discribe it, please. In 1st post i didn't see the how we use something with value 12.
Sapher_Jalt Posts: 17 Rating: (1)
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