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What's a local variable?

Created by: Import-User-1 at: 12/30/2008 11:50 PM (3 Replies)

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12/30/2008 11:50 PM	Rate (0)
Import-User-1 Gold Member Joined: 8/10/2005 Last visit: 2/7/2022 Posts: 3609 Rating: (28)	Import of a Technical Question of an User Guest Hello! My name´s Manu. I´d like to know....what'sa local variable? for exemplo "= L 5.0" Thanksinadvance Manu.

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12/31/2008 5:17 AM	Rate (0)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 6/3/2023 Posts: 12030 Rating: (2594)	Hello manu. The term "local" in programming generally refers to variables (or registers) that can only be accesses by a certain function or routine, whereas a "global varialble is accessible by all functions in a program. Speciically, in S7 [programming, "L 50" is a register in the local stack of a FC, FB or OB, where temporary values and parameters are stored for the exclusive use of the function.The local stack is re-assigned (values are overwritten) as soon as the function is closed. Here is how the local stack is described in the manual Programming with Step 7, v. 5.4, that you can find in the Simatic Documentation directory of your programming PC.: A.2.3.3 Local Data Stack The L stack saves the following: The temporary variables of the local data of blocks The start information of the organization blocks Information about transferring parameters Interim results of the logic in Ladder Logic programs When you are programming organization blocks, you can declare temporary variables (TEMP) that are only available when the block is executed and are then overwritten again. Before you access the local data stack for the first time, the local data must be initialized. In addition to this, every organization block also requires 20 bytes of local data for its start information. The CPU has a limited amount of memory for the temporary variables (local data) of blocks currently being executed. The size of this memory area, the local data stack, is dependent on the CPU. The local data stack is divided up equally among the priority classes (default). This means that every priority class has its own local data area, thus guaranteeing that higher priority classes and their OBs also have space available for their local data. Hope this helps, Daniel Chartier
	Last edited by: dchartier at: 12/31/2008 6:36 AM Last edited by: dchartier at: 12/31/2008 5:18 AM
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4/30/2017 5:18 PM	Rate (0)
AutoGen_406723 Posts: 4 Rating: (0)	Dear Dchartier, Thoses Local variables , can you tell me why I will use them and not Temp variables is they are equal to 0 once the bloc is closed ? Thank you
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5/1/2017 8:23 PM	Rate (1)
Dongerpure Bronze Member Joined: 3/8/2011 Last visit: 5/17/2023 Posts: 262 Rating: (19)	AutoGen_406723 Dear Dchartier, Thoses Local variables , can you tell me why I will use them and not Temp variables is they are equal to 0 once the bloc is closed ? Thank you Hello Autogen These local variables are temp variables if they are not assigned with symbolic address then you see them as example L 2.0 and in some situations you have to use the Local address directly. they don't retain the values out of the function.
	Last edited by: Dongerpure at: 5/1/2017 8:23:56 PM If this post helped you, you may use the Rate-button
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