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DP communications between CPUs

Created by: picengineer123 at: 3/8/2010 5:28 PM (5 Replies)

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3/8/2010 5:28 PM	Rate (0)
picengineer123 Posts: 95 Rating: (0)	I have been searching the fourms and reading threads regarding DP communications between CPUs. It is said often that you cannot have two masters on the same profibus network. In order to transfer data, you need to use a DP/DP coupler. I tried an experiment and built a project with a CPU 417-4 and a CPU 414-3 PN/DP. I put both CPUs DP slots on the same profibus network. I configured a connection in NetPro and compiled. It did compile. So I am curious as to why the software allowed the configuration? I can add profibus modules to the 417 cpu, so is it possible to connect these additional profibus networks to another PLCs master network for communication, assuming my experiment wont actually work. John
picengineer123 Posts: 95 Rating: (0)	Last edited by: O_Moderator at: 3/9/2010 11:11 AM new subject after splitting from /tf/WW/en/Posts/37968#top
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3/10/2010 8:58 AM	Rate (0)
Hulzhex Gold Member Joined: 8/25/2005 Last visit: 10/5/2024 Posts: 1162 Rating: (111)	Hello picengineer123, let's try to make it more clear. There are different kinds of communication which could be established via PROFIBUS. There is the communication between a DP-Master and his DP-Slave. A DP-Slave could communicate only with one DP-Master directly. Between the PLC's another kind of communication could be established. It is a communication between to partners with equal rights. This kind of communication could be configured within netpro between two S7-400 CPU's. This will not be a cyclic communication. I found the following examples within this pages. Not exactly your configuration but I hope it will be helpfull for understanding. Sample program: S7 communication with the blocks SFB14 ("GET") and SFB15 ("PUT") with S7-400 SIMATIC Net QuickStart Best regards Sabine

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3/17/2010 8:48 PM	Rate (0)
picengineer123 Posts: 95 Rating: (0)	Hulzhex Thanks for the input. I was aware that you an connect CPs on a single profibus network, but what about the port on the CPU? In my example I have several CPU 417s and a 417H. There are CP443s for other communications but this customer wants to share data over profibus. We are going to use a DP to DP coupler as needed, but wonder if it was possible as I described. thanks again for your input John
picengineer123 Posts: 95 Rating: (0)
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3/18/2010 8:38 AM	Rate (0)
Hulzhex Gold Member Joined: 8/25/2005 Last visit: 10/5/2024 Posts: 1162 Rating: (111)	Hello picengineer123, please try to make the same configuration within netpro as descriped for the internal DP-Port of your CPU. You will see that it is possible to establish the configuration. So it will work. Good luck Sabine

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3/18/2010 1:16 PM	Rate (0)
picengineer123 Posts: 95 Rating: (0)	hulzhex I agree Netpro will allow to CPUs to be placed on the same profibus network via their onboard ports, not additional CP cards. However, it is said in many placed on the support site that two class I masters cannot be on the same bus and the CPU is a class I master, unlike a PC/PG which can be a class II master. Also, a fellow from Germany, not a Siemens guy, but an experienced Siemens programmer, looked at the project (the cause of this thread) in which the Profibus ports on the CPUs were connected together. He immediately said it will not work. In this instance, we had the system configured in Step 7 as connected and there were no errors. So, the question still remains for me, what is the definitive answer regarding multiple CPUs on the same Profibus network, will it work? regards John
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3/18/2010 2:10 PM	Rate (0)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 12/4/2024 Posts: 12300 Rating: (2691)	picengineer123 However, it is said in many placed on the support site that two class I masters cannot be on the same bus and the CPU is a class I master, unlike a PC/PG which can be a class II master. So, the question still remains for me, what is the definitive answer regarding multiple CPUs on the same Profibus network, will it work? John Hello John; Sorry, either you have misread the information you looked at on the support site, or it was not very clear. Profibus-DP supports basically3 modes of communication: Master-slave cyclic comms (configured data exchange between master and slave) master-slave acyclic (for diagnostic and parameter exchange purposes), and master-master acyclic comms. For this last type there is an embedded token-passing mechanism between masters that share the same physical bus. Look at the following attachment, from the Profibus International dowload pages: http://www.profibus.com/downloads/ It illustrates the token-passing scheme between masters, be they class 1 or class 2 masters on the bus. You will find a lot more information on Profibus on that webpage, from the original source, so you can be sure it is correct. However, on one importantpoint you are right: integrated DP-ports on the Siemens CPUs cannot be used to directly interface data between S7 PLCs; for that you need to establish FDL connections between Profibus CPs and use specialized FBs. The original reason for that was that Profibus-DP was seen as a high-speed, low data amount nework for factory automation; it was feared that acyclic exchanges would slow the bus down to an unacceptable level. I am not surprised to see that Netpro allowed configurations between CPUs. But have you tried programming Usend/URcv or BSend/Brcv blocks? See what happens when you try to use the Netpro Profibus connection... Note however that you can use ther MPI ports of the same CPUs with the same functions and it will work, although at a slower speed rate. Hope this helps, Daniel Chartier Attachment Pbus_MMaster.JPG (151 Downloads)
	Last edited by: dchartier at: 3/18/2010 2:13 PM
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