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I/O access error when a DP node dies.

Created by: mhkocak at: 1/14/2010 3:37 PM (4 Replies)

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1/14/2010 3:37 PM	Rate (0)
mhkocak Advanced Member Joined: 1/8/2009 Last visit: 5/30/2023 Posts: 43 Rating: (0)	Hello, I am a new Profibus user. I am testing what would happen if a node goes offline. There is only a CPU and a DP slave drive in the configuration. In HW configurator, I used I address 288 and Q adress 288 for DP slave communication. And I used these addresses in my sample program as PIW , PQW. After I see communication is OK, I removed DP cable form slave and checked the behaviour of PLC After loading OB82,85,86 and 122 now PLC doesnt stop when I disconnect DP slave. But SF led is on. In Module Information- Diagnoctic Buffer I saw "I/O access error "s. I think in every scan PLC adds this error in buffer. - Is there a way to disable this error. - Why PLC can not access this I/O addresses? - Is there a way to say to CPU " Dont check this node is online or not, I want to make it offline permanently" Thank you.. mhkocak

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1/14/2010 4:19 PM	Rate (0)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 5/30/2023 Posts: 12025 Rating: (2594)	mhkocak Hello, I am a new Profibus user. I am testing what would happen if a node goes offline. - Is there a way to disable this error. - Why PLC can not access this I/O addresses? - Is there a way to say to CPU " Dont check this node is online or not, I want to make it offline permanently" Hello mhkocak; When you configure a slave's module addresses over Profibus-DP, you are placing these addresses on a cyclic request from the DP-master, which proceeds independantly of the main CPU scan. Since there is no reply from the disconnected slave, the slave's diagnostics are being requested by the master, and the module addresses show I/O access errors because you must not use the present values (either the last one accessed, or zero) to make decisions in your program. The way to say to the CPU (actually, the DP-master interface)do notpoll this node anymore until I tell you to is to use SFC12, as shown in the following FAQ (see the downloadable project included): http://support.automation.siemens.com/WW/view/en/15014658 Hope this helps, Daniel Chartier

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1/14/2010 5:12 PM	Rate (0)
mhkocak Advanced Member Joined: 1/8/2009 Last visit: 5/30/2023 Posts: 43 Rating: (0)	Hi, Thank s for your reply. I tried SFC12. It enables and disables a slave node. But "I/O access error" s still existing. When I disable a node with SFC12, Because I use DP I/O address area of this slave node, PLCs SF led turns on and I get "I/O access error". Do you have any idea about this? mhkocak

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1/17/2010 4:57 PM	Rate (0)
jklm Platinum Member Joined: 12/22/2006 Last visit: 1/25/2022 Posts: 1742 Rating: (303)	Hello, Because you have decided to disable the slave by software usingSFC12, it should be easy to block the call to the program using info from that slave, or to conditionnaly jump over these instructions in the software.
	Best regards jklm Suggestion was helpful? Feel free to rate it.
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1/22/2010 10:23 AM	Rate (0)
H-H Platinum Member Joined: 7/2/2008 Last visit: 3/14/2023 Posts: 928 Rating: (303)	Hello mhkocak, The I/O access error is a synchronous error. There's SFC36 "MSK_FLT" for masking synchronous errors which means that the CPU will not trigger OB122 or OB121in a certain priority class. You can filter which error to be masked and which to be not. For unmasking errors you will have to use SFC37 "DMSK_FLT". You didn't mentionwhether you have S7-300 or S7-400 but be careful and read the help of SFC36 (If you are going to use it)carefullybecausethe behavior of S7-300 differs to behavior of S7400. You can try it as it's there but honestly I never used it and will never do. I always prefer that all errorsget registered in diagnostic buffer and always have the SF LED to remind the maintenance guys ''You have a problem - Solve it''. Best regards. H-H

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