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3/1/2013 8:07 AM | |
Posts: 81 Rating:
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Hello, please find attachment. . Here my 300 plc is connected to field I/Os over profibus network & CP 342-5 card is act as a slave connected via y-link to 400 system over optical fiber network. I made Cp342-5 slave device. In master configuration, for exchange of data i installed .gsd file of Cp342-5 but in this i have found that (plz see attachment)consistency 1 byte/word & total consistency with DI,DO,AI & AO options. What is difference betweenconsistency 1 byte/word & total consistency?? What should i use for data mapping from slave to master & vice-versa?? regards, manoj
Attachment11.pdf (261 Downloads) |
3/1/2013 1:01 PM | |
Joined: 9/27/2006 Last visit: 2/15/2025 Posts: 12336 Rating:
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Hello Manoj; The following document explains (in ageneral view) what is consistent data and how specifically it is maintained in Profibus-DP communictaions. Consistent data in S7-400, summary of mechanisms If you already understand the way a PLC operates, you know that at the beginning of the scan the CPU starts by reading all input values from its digital input modules and copies these input bytes in the Input Image table, as a consistent whole; then you run your program on the contents of the image table. You don't see any changes that could be happening in the meantime in the field (and you don't want to), Once the program has been run, the outputs calculated by the program are then copied to the Output Image table, and at the end of the scan all the digital output modules are updated at once, consistently. This use of consistent data ensures program stability over the scan cycle. Imagine that in your program you evaluate the status of an input bit in various networks, and that the value of this input address changes during the scan cycle, you could end up with a very erratic behaviour of your PLC program. The same definition applies with communications data transfer (on Profibus-DP in your case). Sometimes it is required that specific data transfermust not be interrupted and that bytes are transfered together as a single (consistent) telegram. I have only one example where it is absolutely required, in the PZD transfer mechanism of Siemens drives (for read/writing of drive prameters).But you can choose to have consistent data use anywhere in your Profibus-DP configuration. When data in the Profibus configuration has been defined as "consistent over total" you must use the functions SFC15 "DPRD_DAT" and SFC14 "DPWR_DAT" to input or output the consistent data; if the data is configuered as consistent over unit, you can read and write the data with MOVE (Load/Transfer) instructions in your program, as if you were accessing an analog value form the field. Hope this helps, Daniel Chartier |
Last edited by: dchartier at: 3/1/2013 1:14 PMLast edited by: dchartier at: 11/18/2020 02:16:39 |
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