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S7- Limitations of calling FBs from FCs

3/26/2007 12:54 PM	Rate (0)
Techy Posts: 86 Rating: (2)	Hello All, I am facing a wierd situation. Whenever I call a standardmodbus FB180from a FC it is not working. However once I shift the same network to OB1 it works. Is this related to nesting? Do I need to increase the local data priority class settings? It's showing 758 for Priority 1 which I believe is OB1? Are there any limitations as to how many FBs /DBs that can be called from an FC? Any right direction data pointers are welcome Techy
Techy Posts: 86 Rating: (2)	Last edited by: Techy at: 26.03.2007 12:58
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3/26/2007 5:14 PM	Rate (0)
Denilson Pegaia Diamond Member Joined: 9/23/2005 Last visit: 12/24/2025 Posts: 4434 Rating: (1487)	Hi, Generally, you can call a FC / FB from anywhere. However, you must take care about these limitis: 1 - The FB/FC that call (Father) doesn't exced its maximal code size (e.g. 16k for S7-300). 2 - There is a maximal number of the cascated call (I don't remember the number, but it is big). I.e. FC 1 call FC2 that call FC3...FCn. 3 - The total of the temp variables of all FC/FB called ifrom an OB in one momment must be in accordance witch the HW configuration. For example OB1 call FC1 that call FC2; OB1 need 20 bytes, FC1 100 bytes and FC2 1000 bytes; the HW config must alloc at leas20+100+1000=1120 bytes to OB1.
	Denilson Pegaia Siemens Industry Sector Technical Support
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3/26/2007 7:35 PM	Rate (0)
Techy Posts: 86 Rating: (2)	Thanks Pegaia. One quick question . Does this mean I have to change the OB1 allocation of 758 to 1120 if I were to go by your example?
Techy Posts: 86 Rating: (2)
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4/2/2007 6:04 PM	Rate (0)
Denilson Pegaia Diamond Member Joined: 9/23/2005 Last visit: 12/24/2025 Posts: 4434 Rating: (1487)	Hi, You are right.
	Denilson Pegaia Siemens Industry Sector Technical Support
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