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Profibus and HMI - Telegrams

Created by: danhsistech at: 1/22/2013 2:49 PM (6 Replies)

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1/22/2013 2:49 PM	Rate (0)
danhsistech Advanced Member Joined: 12/15/2011 Last visit: 3/15/2024 Posts: 11 Rating: (0)	Hi all who can tell me know what the Profibus telegrams when S7 300 PLC communication with HMI via Profibus ex. SD? SSAP DSAP ? DU?... anybody help me? Attachment Profibus.pdf (297 Downloads)
	Last edited by: danhsistech at: 1/22/2013 3:42 PM
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1/22/2013 3:41 PM	Rate (0)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 3/17/2025 Posts: 12344 Rating: (2707)	Hello danhsistech; The Profibus-DPtelegram sections you refer to are part of the cyclic master/slave communications between a master class 1 (a controller, PLC..)and a slave. In that case the data exchange is built based on the available registers in the slave (selected from its gsd file) and the Profibus configuration downloaded to the master before the start of exchanges 9and sent by the master to each slave at the beginning of exchanges). The HMI (or programming console, or SCADA computer) is a master class2 in Profibus nomenclature, however. This is how the same document described these: The class 2 master is usually a configuration device, perhaps a laptop or programming console, and is provided for commissioning, maintenance, or diagnostic purposes. It acts like a “supervisory” master in that it can actively communicate with class 1 masters and their slaves, in addition to its own slaves, but usually only for the purpose of configuration, problem diagnosis, and data/parameter exchange. That is, class 2 masters may only briefly take over control of a slave. All exchanges between a class 2 master and class 1 master originate with the class 2 master. ... To illustrate the idea of communication between masters in a ProfiBus DP system, a class 1 master cyclically exchanges data with all of the slaves assigned to it, one at a time, according to its list of assigned slaves taken from the master record. At the end of this data cycle, additional time (gap time) is allotted to provide for acyclic communication between a class 2 master and the same slaves. During this time, the class 1 master will pass a token to the class 2 master granting it bus access rights. The class 2 master which currently holds the token has the opportunity to exchange data with all the slaves within a specific period of time called the token half-time or token hold-time (TH). The class 2 master may then proceed to read data or diagnostic information from any of the slaves, and then at the completion of its cycle, it will pass the token back to the class 1 master. So masters class 2 use the same Profibus-DPtelegram format, but the items in the telegram change to follow the present needs of the master class 2: An HMI will need to update different masters or slaves to fill its input/output fields, for example; the master class 2 will build its telegram with internal function blocks designed for its communication needs at the moment.The telegrams will be sentonly when the HMI recieves the token on the bus, and data requested will change every time it talks to masters class 1 or slaves on the bus. Hope this helps, Daniel Chartier
	Last edited by: dchartier at: 1/22/2013 3:45 PM
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1/22/2013 4:38 PM	Rate (0)
danhsistech Advanced Member Joined: 12/15/2011 Last visit: 3/15/2024 Posts: 11 Rating: (0)	ex My HMI have tag (address MW 0) what the telegrams when HMI access data from PLC S7 300 via profibus. i was capture a frame data 68 44 44 68 81 87 5c 14 14 f1 5c 32 03 00 00 00 01 00 02 00 2f 00 00 04 08 ff 04 00 08 a7 00 ff 04 00 08 a6 00 ff 04 00 08 a5 00 ff 04 00 08 a4 00 ff 04 00 08 a3 00 ff 04 00 08 a2 00 ff 04 00 08 a1 00 ff 04 00 08 a0c0 16 I know a7 a6 a5 a4 a3 a2 a1 i value but i don't know where is address of data ex MB0, MB1, MB2... in the data frame Attachment Untitled.jpg (182 Downloads)

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1/23/2013 10:28 PM	Rate (0)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 3/17/2025 Posts: 12344 Rating: (2707)	Hello anhsitech; What software/hardware did you use to capture this Profibus frame? Whenever I had the chance I would borrow a collegue's Procentec equipment to use the scope screens and evaluate signal strength and diagnose problems on the bus, but I have never studied telegrams as such. I hope someone here has an answer to the question, it would be an enlightening bit of information. Regards, Daniel Chartier

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1/24/2013 9:10 AM	Rate (1)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 3/17/2025 Posts: 3042 Rating: (1061)	Hello danhsistech as Daniel already said, when the Class 2 master HMI has the token, it willsend it's request as a - well let's say - "general" Profibus DP telegram to the PLC. In thiscase it is an SD2 type DP telegram (= telegram with variable information and lenght) as the SD type value is68hex (first byte in telegram and explained in the pdf that you had attached to your first post). What a Siemens HMI does though is to use the S7 protocol to talk to the S7 PLC and this is a Siemens proprietary protocoland you won't find the makeup of the DU (data unit) explained in the Profibus Standards (FC, SSAP and DSAP are outside of the ProfibusDP defined ones too and Siemens specific). While I'm not to sure why you want to decipher the S7 protocol (sheer curiousity perhaps?), you will find some info on it with Google search. I hope this helps
	Last edited by: fritz at: 1/24/2013 9:11 AM Cheers fritz The advice and opinion given in this thread is that of the author and does not necessarily reflect the views of I S Systems Pty Limited. To find out how I S Systems can help you with your automation needs please visit www.issystems.com.au.
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This contribution was helpful to 1 thankful Users hdhosseini

1/25/2013 5:40 AM	Rate (0)
danhsistech Advanced Member Joined: 12/15/2011 Last visit: 3/15/2024 Posts: 11 Rating: (0)	Hi fritz I want replace old HMI serial to new HMI serial but when upload form old HMI - i have a images file. i can't dowload to new HMI serial.

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1/25/2013 5:42 AM	Rate (0)
danhsistech Advanced Member Joined: 12/15/2011 Last visit: 3/15/2024 Posts: 11 Rating: (0)	hi dchartier I use a cable RS232 - RS485 and a software "Eltima Serial Port"

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