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Communication with drive

Created by: petermat at: 3/4/2009 11:19 AM (3 Replies)

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3/4/2009 11:19 AM	Rate (0)
petermat Posts: 15 Rating: (0)	How does PLC communicate with drive? What exactly does it need to be set so data will be send to correct address? So far I know I need to set same profibus value for drive in step7 and in drive itself. What I am curious about is: 1) what does address range mean when setting them(ex starting addrress 336 + 6 words)? 2) how do we tell PLC what word does it need to send to drive? 3) does PLC write to drive status word or ....? 4) does drive send any data to PLC, or it just writes into its status word and PLC reads it? 5) when PLC knows that it needs to read feedback from drive (I assume it reads directly from drive status word)? These are just some questions that I can think of at the moment, Feel free to add anything that is relevant for this topic. If there is any good resource that will help me to understand this, please point me to it. Thanks, Peter
petermat Posts: 15 Rating: (0)
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3/4/2009 2:54 PM	Rate (0)
dchartier Grandmaster Joined: 9/27/2006 Last visit: 12/24/2025 Posts: 12472 Rating: (2722)	Hello Peter; 1) what does address range mean when setting them(ex starting addrress 336 + 6 words)? Each drive family has a different telegram format, it would be easier to answer with information on the specific drive you are using, and the telegram format selected. But basically each word will have a specific content that you will find in the documentation of the Profibus interface for that specific drive. 2) how do we tell PLC what word does it need to send to drive? Since each word of the telegram contains specific information (Control Word, Speed Reference…) then all you need to do is to write the appropriate value to the address specified by the HWConfig editor. For example, say the first word of your specified drive is the drive’s control word, then you would write the correct command value to PQW336. If the Speed Reference occupies the second word, then write that value to PQW338. Use the MOVE instruction (in LAD) to write a value to a word address. 3) does PLC write to drive status word or ....? No, the PLC only reads the PIWxxx addresses of the status words from the drive. 4) does drive send any data to PLC, or it just writes into its status word and PLC reads it? Since the drive is a slave on the Profibus-DP network, it is a passive node. It cannot write by itself on the network; it can only reply to a request by the Profibus master. So the status word is continuously updated on the drive by the drives operating system. The PLC reads it cyclically everytime it communicates with the drive as a Profibus master 5) when PLC knows that it needs to read feedback from drive (I assume it reads directly from drive status word)? See reply to point 4) So go back to the documentation on the Profibus-DP interface for your specific drive, study the telegram structure between master and slave, and associate every word reserved in the HWConfig for that drive to the information it will transfer between master and slave. Hope this helps, Daniel Chartier

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3/4/2009 3:00 PM	Rate (0)
Wizard Diamond Member Joined: 4/24/2006 Last visit: 12/24/2025 Posts: 9094 Rating: (1202)	Dear petermat, It's important to know which PPO type you want to communicate. Here are some links, perhaps they are useful: http://support.automation.siemens.com/WW/view/en/8894363 http://support.automation.siemens.com/WW/view/en/30558965 http://support.automation.siemens.com/WW/view/en/32120569 http://support.automation.siemens.com/WW/view/en/6586565 Best regards, Wizard

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3/8/2009 9:40 PM	Rate (0)
petermat Posts: 15 Rating: (0)	Thanks for the responses, dcharties and Wizard. I was more interested in the general steps for reading writing than for the actual drive. After I have gone to the project more thoroughly, I see that PLC reads/writes from/to drive with SFC14 and SFC 15, which I believe are just wrappers for MOVE command. I think I now have all the pieces together. Now its only a matter reading documentation about specific telegram signature drive uses. Thanks again, Peter
petermat Posts: 15 Rating: (0)
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