Skip to Content

Register Login

Industry Online Support

Technical Forum

Navigation

Data block Pointer

Created by: alifaez at: 8/29/2011 11:27 PM (11 Replies)

Rating (5)

Thanks 0

Result pages:: |; 1 | 2; |

12 Entries

Entries per page: 10 | all

8/29/2011 11:27 PM	Rate (0)
alifaez Posts: 36 Rating: (0)	Hello everybody Why we must use TEMPORARY variables in FC or FB as data block pointer?
alifaez Posts: 36 Rating: (0)
Suggestion To thank Quote Answer

8/30/2011 8:10 AM	Rate (0)
Darius Platinum Member Joined: 9/28/2005 Last visit: 5/2/2023 Posts: 2957 Rating: (242)	Hello, alifaez Hello everybody Why we must use TEMPORARY variables in FC or FB as data block pointer? What do you mean by that ? You are not forced to use TEMPORARY variables as data block pointers. I really don't understand your question.
	Best regards, Darius
Suggestion To thank Quote Answer

8/30/2011 8:15 AM	Rate (0)
Aret Posts: 2348 Rating: (259)	You mean in case OPN DB[#DB_num] why #DB-num is accepted as TEMP, but not as INPUT or i miss something?
Aret Posts: 2348 Rating: (259)
Suggestion To thank Quote Answer

8/31/2011 2:05 AM	Rate (0)
alifaez Posts: 36 Rating: (0)	Hello Aret Thanks for your attention Yes that is just what i mean,why this pointer could not be transfer in any other kind of variables like static,etc.?
alifaez Posts: 36 Rating: (0)	Last edited by: alifaez at: 8/31/2011 2:07 AM
Suggestion To thank Quote Answer

8/31/2011 2:12 AM	Rate (0)
alifaez Posts: 36 Rating: (0)	Hello Darius Thanks for your attention I can not use any other kind of varible types like STATICas data block pointer.
alifaez Posts: 36 Rating: (0)
Suggestion To thank Quote Answer

8/31/2011 7:29 AM	Rate (0)
Darius Platinum Member Joined: 9/28/2005 Last visit: 5/2/2023 Posts: 2957 Rating: (242)	Hello, alifaez Hello Darius Thanks for your attention I can not use any other kind of varible types like STATICas data block pointer. Well actually if we speak about FC then you only have TEMP variables, no STATIC. If you use FB and you have static INT variable starting at L0.0 then you can use it as [code] OPN DB[#LW0] [/code] Therefore you can't use IN variables for that.
	Best regards, Darius
Suggestion To thank Quote Answer

9/5/2011 3:00 PM	Rate (0)
alifaez Posts: 36 Rating: (0)	Hello Darius If we want to use pointer for data blocks in an FB ,we must use TEMP.variable too.We are not able to useSTATIC variable either,why?
alifaez Posts: 36 Rating: (0)
Suggestion To thank Quote Answer

9/5/2011 3:35 PM	Rate (0)
Darius Platinum Member Joined: 9/28/2005 Last visit: 5/2/2023 Posts: 2957 Rating: (242)	alifaez Hello Darius If we want to use pointer for data blocks in an FB ,we must use TEMP.variable too.We are not able to useSTATIC variable either,why? As I said you can use STATIC variables but use L memory area for that. Actually I don't know why you can use name of STATIC variable, but workaround of that is L memory area.
	Best regards, Darius
Suggestion To thank Quote Answer

9/5/2011 4:02 PM	Rate (1)
Aret Posts: 2348 Rating: (259)	Well, that's the way i see it Imagine you have CALL FB1, DB1 When you write inside FB1 OPN DI[#dn] // #dn is static variable actually that means OPN DI[DB1.dn] But to getDB1.dn you should write 1 to DI register (actually L DB1.DBW0 is OPN DB1+L DBW0). But from the other hand you should write acquired DB1.dn value to DI register. Of course such logic can be implemented step-by-step, but requires OPN to be macro and in S7 environment OPN is single command already. Looking on DB register - same logic can be applied, because DB register may be used on calling FB with complex data type. Summary: guess it was complication Siemens didn't want to implement - so they set a restriction on using TEMP variables only thus hitting target both with FC and FB.
Aret Posts: 2348 Rating: (259)
Suggestion To thank Quote Answer

9/6/2011 2:01 PM	Rate (3)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 6/8/2023 Posts: 2968 Rating: (1025)	Hello alifaez let me start by stating that you can use an FB's STAT variable as a DB pointer. This is however only possible if you remove the Multi Instance capability from the FB when you create it. By default, Multi Instance capability is ticked when you create an FB, in which case Step 7 will NOT allow you to use a STAT variable as a DB pointer. Even though I suppose the Step 7 Editor could be changed to able to handle/allow this, it won't be an easy fix for Siemens as AR2 is taken into accountfor all accesses to FB variables with Multi Instance capability(AR2 contains the Multi Instance offset). What you can do though in a Multi Instance capable FB is use for example "DIW xyz" directly as the DB pointers address. Note that this though means that the FB will NOT work if called as a Multi Instance. I hope this helps and attached is a pic with an example for both cases which shallhelp in making sense out of what I'm trying to say. Attachment FB STAT variable as DB Pointer.jpg (715 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.
Suggestion To thank Quote Answer

|

Share this page:

Share this page on...

Follow us on