3/24/2014 8:21 AM | |
Joined: 10/7/2005 Last visit: 9/20/2024 Posts: 3021 Rating: (1054)
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Hello azi1984 every I/O device canhave its own update time in Profinet. If automatic update time calculation is selected in Step 7 (as it is in your case), Step 7 will take into account the numberI/O devicesand their cyclic data volume and assign what it deems to be the fastestupdate time for every I/O device (and use 2ms as the bare minium as it is also the case in your setup). If you have time critical data, you can selectively assign faster I/O update time to those I/O devices (as well as giving other I/O devices their own slower I/O update time). In this case, you need to do a bit of homework though to avoid potentially overloading your Profinet network (bear in mind that once you tell an I/O device how fast you want it to update, it will attempt to do so). PI hassome good free of charge Profinet Design guides as well as a Network load calculation toolwhich you can get from http://www.profibus.com/nc/pi-organization/regional-pi-associations/south-east-asia/downloads-and-media/downloads/profinet-installation-guide/display/. The Siemens Profinet System Description is also well worth a read on this subject and the online Determining the PN response time, the HMI update time and the HMI operating time for typical PROFINET IO configurations calculator may come in handy too. As for your X208 SCALANCE switch: It too is an I/O device and will as such have an I/O update time. Step 7 though by default gives it a slow update time of 128 ms as all you'd get from it are non time critical diagnostic data. It's "slow" 128ms update time has though nothing to do with thespeed of the switch forwarding PN I/O data. Each X208 will nonethelss introduce a delay and how long the delay is dependsif you spent more money and bought the IRT version (which supports "cut through") or went for the cheapernon-IRT version (which only supports "store and forward"): - IRT X208 type: 7 micro second (it only evaluates the first 6 Bytes and then starts "spitting out" the PN I/O data frame at the correct port). - Non-IRT X208 type: ~10 micro seconds for a 64 Byte long frame and ~130 micro secondsfor a 1500 byte long frame (both at 100Mbps, the whole frame is received firstwith "store and forward" before being"spatout" again at the correct port). I hope this helps |
Last edited by: fritz at: 4/4/2014 5:10 AMrevised X208 delay paragraph to distingiush between IRT and Non-IRT versions (thanks Falk for making me aware of the previous ambiguity) Cheers |
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10/18/2023 1:22 PM | |
Joined: 5/30/2014 Last visit: 9/18/2024 Posts: 147 Rating: (18) |
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