9/1/2011 3:35 PM | |
Joined: 3/21/2006 Last visit: 10/7/2024 Posts: 10229 Rating: (1181) |
Hello, Take a look at What are the conditions for assigning the addresses of I/O modules (central or distributed) to an S7 CPU? Best regards, Hristo Mihalev |
9/2/2011 1:59 PM | |
Joined: 10/7/2005 Last visit: 10/21/2024 Posts: 3024 Rating: (1054)
|
Hello Gssc1414 my personal preference is to make the Process Image as Iarge as needed to cover all I/O's and the main reasons for this are: - All I/O's can be accessed directly on a bit level (I would always make sure that the Process Image is set to be at least large enough to cover all digital I/O's) - All I/O's are automatically synchronised with the scan and consistent (see HERE for more on consitent data) - By doing only Process Image based access you don't flood your CPU diagnostic buffer with OB122 calls in case a remote rack/device is switched off or a card fails (any peripheral access will otherwise lead to an OB122 call every scan, make sure to set OB85 to either "only for incoming and outgoing errors" or "no OB85 call" in the CPU properties, otherwise you get OB85 Diag buffer flooding every scan) - If you need direct peripheral access for whatever reasons,you can still do it too (see also HERE for more on the issue of peripheral addressing). To bear in mind though is: - The update of the Process Image takes time too (the bigger the image, the longer it takes), see chapter 6.2.2 of the SIMATIC S7-300 CPU 31xC and CPU 31x: Technical specificationsfor more. Note that only the I/O's are updated in the Process Image that exist as physical I/O's (i.e. the gaps in the I/O address range are NOT updated and do NOT consume Image update time) - Increasing the Process Image consumes more work memory. Thismemory will (somewhat obvious) be consumed for the whole I/O range range from 0 to highest byte, irrespective ifphysicalI/O cards exist for the address or not (a tinyprice to pay though in my opinion). That's all I can think of and I hope it helps |
Last edited by: fritz at: 9/2/2011 2:43 PMfixed more typos Last edited by: fritz at: 9/2/2011 2:03 PMtypos Cheers |
|
This contribution was helpful to4 thankful Users |
7/23/2013 8:37 AM | |
Joined: 4/24/2009 Last visit: 8/20/2024 Posts: 2682 Rating: (135) |
New question splitted to process image update error after adding extra remote stations Best regards O_Moderator |
Follow us on