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Maximum local data in FC

Created by: Simotion at: 6/20/2008 9:58 AM (4 Replies)

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6/20/2008 9:58 AM	Rate (0)
Simotion Posts: 223 Rating: (1)	How many temp-variables can I use as maximum in a function without having problems. What if I cross that limit? Will the system tell me, or won't it and will I experience other problems,
Simotion Posts: 223 Rating: (1)
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6/22/2008 1:03 PM	Rate (0)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 1/21/2026 Posts: 12481 Rating: (2722)	Hello simotion: The local stack size id dependant on the CPU yoou are using; so: This is extracted from the manual Simatic CPU 31xC and CPU 31x, Technical data: Local Stack: S7 CPUs change to STOP mode if the permitted L stack size for a program isexceeded. Test the L stack (the temporary variables) in your program. CPU 312C: 256 bytes max CPU313C: 510 bytes max CPU 315-2DP: 1024 bytes max… I presume that OB121 (Programming Error OB) will prevent you from going to STOP mode, but the offending block will probably never be executed. Hope this helps, Daniel Chartier
	Last edited by: dchartier at: 6/22/2008 1:04 PM
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9/12/2008 10:40 PM	Rate (0)
OlafS1 Experienced Member Joined: 6/1/2006 Last visit: 10/18/2025 Posts: 144 Rating: (14)	Hello Simotion, the local stack size is limited and specific to the used CPU modell. You could use STEP7 to determine the maximum used L-Stack. Do a Cross Reference on your program and check for every execution level (means every used OB) the number in the brackets. This is the maximum L-Stack usage for your program. Compare this to your permissible L-Stack size. If your used L- Stack is below that value, you're fine. If not off load some L-stack values to either global (not good style) or DBs to reduce the used L- Stack. Try to reduce the nesting depth.

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9/25/2008 9:20 AM	Rate (2)
H-H Platinum Member Joined: 7/2/2008 Last visit: 12/21/2025 Posts: 929 Rating: (309)	Dear Daniel, I think the CPU will go toSTOP regardless ofany OB. Ithink OB88 might be the one for errors regarding local data but not the error of exceeding the length of local data. best regards. Attachment Local data & OB88.pdf (909 Downloads)

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9/25/2008 1:49 PM	Rate (0)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 1/21/2026 Posts: 12481 Rating: (2722)	Thanks H-H, very good point. I'll have to study this more attentively. Especially calls to OB88. Regards, Daniel Chartier

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