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S7-1200 Program size effecting functionality!

Created by: kevsticle at: 12/16/2009 11:26 AM (9 Replies)

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12/16/2009 11:26 AM	Rate (0)
kevsticle Posts: 8 Rating: (0)	Hi, We have spent the last few months developing a project that has become quite large. We have found that the RS485 module stops talking to our ModBus devices when we download the full program. If we cut down on the number of function blocks inserted it starts working again!! We have tried different sizes and it seems to be total of memory or something rather than actual function block count. We have also tried different working function blocks.There is about 10k of work memory left and not even half the load memory is used! Also, as we are tight on memory it would be nice if somebody has any advice on what memory actually gets used for what when a project is compiled so that we can try to do some optimising. We have checked that we are well inside the maximum cycle time. The comms show no errors and the lights flash but the remotes get no useful data. There are no diagnostic errors. Any advise would be greatly appreciated as we are now stumped...
kevsticle Posts: 8 Rating: (0)
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12/16/2009 1:36 PM	Rate (0)
Robster Gold Member Joined: 5/28/2008 Last visit: 10/23/2024 Posts: 1343 Rating: (141)	Hi, so far I understood you are the opinion that function block stop working without error, am I right? Mh, strange. Can't believe that. Let's try to summarize the facts: - there is enough work memory? - cycle time is less the 150ms? - how is your program sequence? My ideas: If cycle time causes an error, then CPU stops and red LED is on. You can adjust cycle time in hardware configuration of PLC. So it is possible to get more the 150ms. What also can be is a faulty program sequence. Maybe program hangs up at one point, because of a wrong or lost condition. When you programmed stepwise, you should be able to find out at which step program hangs up. If not, it makes it difficult to find fault. Third idea: you have some function blocks with the same number, why ever, it can be compiling has overlooked that. What you also can try is a Memory reset (MRES) of PLC after that download whole program again. So, there is nothing more to my mind at moment. Please try this and report again. regards

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12/17/2009 1:46 PM	Rate (0)
kevsticle Posts: 8 Rating: (0)	Hi and thanks, Load Memory= 62% free Work Memory= 21% free Ret Memory=92%free Cycle Time=42ms, 96ms longest Sequence:- OB1: just sets an init flag OB300: Common code OB310:ModBus comms OB320: Process analogue signals from modbus OB330: Tank level checks OB340: Control some pumps OB350:Control some pumps OB360:Control some pumps OB370:Control some pumps OB380:Control some pumps OB390:Control some pumps OB400:Control some pumps MRES did not help PLC remains in Run I tried adding a counter to the end of each OB and they all count up perfectly - no processing appears to be missed, just broken ModBus! FB no.s checked and renumbered for good measure. Fault remains. Any further ideas?
kevsticle Posts: 8 Rating: (0)
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12/17/2009 3:43 PM	Rate (0)
glubb Posts: 26 Rating: (4)	Hello, looks ok from here... have you checked/traced the return values of the Modbus calls? (error, status, busy) glubb
glubb Posts: 26 Rating: (4)
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12/17/2009 7:55 PM	Rate (0)
kevsticle Posts: 8 Rating: (0)	meant to say, no errors are shown from the comms FB and the busy flagdoesn'teven set for anoticeableamount of time, however the lights flash briefly - you can see its not the correct amount of time and the slavesreceivenothing valid....
kevsticle Posts: 8 Rating: (0)
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12/17/2009 9:35 PM	Rate (0)
glubb Posts: 26 Rating: (4)	just an idea: Easy Book or Manual mentions something about using TSEND, ... only in OB1... Maybe you can give it a try and call the modbus functions from the main OB1... just a guess...
glubb Posts: 26 Rating: (4)
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12/17/2009 11:24 PM	Rate (0)
kevsticle Posts: 8 Rating: (0)	I am sure I read in the forums from a guy who posts a lot and is highly rated that itdoesn'tmatter where you put it, however I shall try this in the morning - thanks.
kevsticle Posts: 8 Rating: (0)
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12/18/2009 9:52 AM	Rate (0)
kevsticle Posts: 8 Rating: (0)	Hi, Ok we just tried that and it stilldoesn'twork. Losing faith in these S7-1200's...
kevsticle Posts: 8 Rating: (0)
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12/18/2009 10:18 AM	Rate (0)
Robster Gold Member Joined: 5/28/2008 Last visit: 10/23/2024 Posts: 1343 Rating: (141)	Do not despair. I think there is a solution for the problem. I think more and more it is a modbus communication problem. I found some links with usefull information. Maybe you should read them and check your system again. Tips for Modbus Multiple MODBUS masters on single 1211 CPU How to use S7-1200 Modbus library with more than one slave S7-1200 MODBUS RTU - how to use it? S7-1200 Modbus Communication Problems

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12/19/2009 10:14 PM	Rate (0)
kevsticle Posts: 8 Rating: (0)	If it is a problem outside of the PLC, how can changing code other than the comms code, with a scan rate that is still very fast, make any difference? I can't see it being a ModBus issue and even if it was, I cannot change the device I am talking to. I have talked to the same modules using Koyo PLC's for years with no problems (Dupline Master Modules).
kevsticle Posts: 8 Rating: (0)
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