6/19/2009 4:47 PM | |
Posts: 116 Rating: (1) |
Hi, Can you tell me at what baud you are communicating between DP master and slave? Regards Paresh |
6/19/2009 10:39 PM | |
Posts: 45 Rating: (0) |
Hi |
Last edited by: gumis at: 6/19/2009 10:40 PM |
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6/20/2009 2:24 AM | |
Posts: 139 Rating: (25) |
The image of the data you posted looks like a token exchange message. |
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6/20/2009 11:24 AM | |
Posts: 116 Rating: (1) |
No, Master passes token to itself if there is no any other master present within network. Master never passes token to slave. Please find the attached image of Profitrace software in which I have highlated such frame. As far as 9.6 Kbps speed is concerned, I still doubt whether you will be able to see exact frames or bytes and I do not know whether Profibus communication is possible at 9.6 Kbps Thanks and Regards Paresh AttachmentProfitrace.zip (301 Downloads) |
6/20/2009 2:22 PM | |
Joined: 10/7/2005 Last visit: 9/23/2024 Posts: 3022 Rating: (1054) |
Hey guys 9.6 Kbps is a supported Profibus DP baudrate. The only difference thatgumis would see at this speed though is a change in the time base of his oscilloscope recording (apart from possibly aslightly "cleaner"square waveform). For your info gumis you will "see" at least 4 messages in your setup per bus cycle which are (am I correct in assuming that this still comprises of one PLC and one PPO3 drive and nothing else?): 1.) SD2 (request) message from PLC to drive (outputs to drive, this will be 13 Bytes long all up with 2 Words of net data for PPO3). 2.) SD2 (response) message from drive toPLC (inputsto PLC, this will also be 13 Bytes long all up with 2 Words of net data for PPO3). 3.) SD1 message (aka FDL status request, PLC "pings" for another master, 6 Bytes long). 4.) SD4 message (token passing, in this case PLC passes token back to itself, 3 Bytes long) For completeness, every so often (e.g is SYNC or FREEZE commands are used or Master enters CLEAR state or periodically at a rate of 3*WDT) you'll also "see" aso called Global control message on the bus (coincidentally also 13 Bytes long and of SD2 type) Nothing else to add since Anchobi said it all and good on him for recognising the captured (Oscilloscope) message as a token passing one (I concur with his assertion as it is too short to be anything else). Cheers Fritz |
Last edited by: fritz at: 6/20/2009 3:43 PMCheers |
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6/21/2009 1:07 PM | |
Joined: 10/7/2005 Last visit: 9/23/2024 Posts: 3022 Rating: (1054) |
Hello again gumis
You need to change the way you are thinking about communication. Any message on the Profibus is always "seen" by all stations. Since the message contains the Destination Address (amongst other things) only the station that has that address will accept it and issue a reply message. While it may not make sense for the Master to send a message on the bus that in this case he himself won't even "see" (unlessof course you have really bad reflections on the bus but lets not discuss this though further) nor will be "answered" by anyone else (as it is technically a message for himself), he'll send this "pass token back to myself" message out anyhow (he has to do it as it is part of Profibus standard that a token passing must take place between masters). Cheers Fritz |
Cheers |
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6/26/2009 2:15 AM | |
Joined: 10/7/2005 Last visit: 9/23/2024 Posts: 3022 Rating: (1054) |
hello gumis allow me toquote myself from an earlier post of this thread to answer your question 1:
As for question 2: Yes it could also be the 6 byte long FDL status request that you captured, please don't "blame" Anchobi for NOT spending hours trying to exactly decipher the oscilloscope screen capture whose resolution is not all that accurate (I give hime a lot of credit for realising that it is NOT the SD2I/O message frame). I hope this helps cheers fritz |
Last edited by: fritz at: 6/26/2009 2:16 AMCheers |
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