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S7-1200 and S7-300 as Profibus PA Slaves

Created by: Rodrigo F. at: 2/3/2022 10:46 AM (3 Replies)

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2/3/2022 10:46 AM	Rate (0)
Rodrigo F. Experienced Member Joined: 11/29/2013 Last visit: 5/21/2024 Posts: 98 Rating: (3)	Hey there, I have several large Profibus DP networks, where the Masters are S7-1517-3 PN/DP (either with the integrated DP interface or through the CM1542-5 communication module). As slaves, I have S7-1200s (through the CM 1242-2 module), S7-300s (through a CP342-5 or directly to a 315-2 PN/PD CPU) and a few S7-200s (probably not relevant, as they will be decommissioned soon). For reliability reasons I would like to change some of these segments to Profibus-PA (it would be useful for me to be able to use long stubs and star topologies without repeaters). It's easy enough to install a DP / PA coupler, but is there any way of making all my DP slave devices compatible with the PA segment? Protocol-wise I know it's the same, so it should work, but as the physical layer and encoding are different imagine the DP modules on the S7-1200/300/200 cannot be directly connected to a PA segment. Any ideas? :) Thanks a lot, Rodrigo

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2/3/2022 11:50 AM	Rate (0)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 11/11/2024 Posts: 12293 Rating: (2691)	Hello Rodrigo; You are right that the Profibus-DP interface of your PLCs cannot be transformed into a Profibus-PA slave interface. The physical layer and the protocol are too different. If you want to go onto details, open the Downloads link at Profibus.com, Profibus International provides official documentation on both protocols. An interesting detail: one of the reasons Profibus-PA can have such extended segment lengths is because the transmission layer MBP (Manchester-coded, bus powered) operates at relatively low speeds, 31,75 kb in the PA segment. 45,45 kb in the DP/PA coupler. On Profibus-DP networks, as soon as you operate at 187,5 kb or less, your segments can run up to 1000m, before the first repeater is required. And if you want star or tree topologies, along with long spur lines in a Profibus-DP environment, Procentec has been proposing Profihub modules for years: https://procentec.com/products/profihub/ So there are ways to emulate a Profibus-PA topology with Profibus-DP networks. Hope this helps, Daniel Chartier

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2/3/2022 12:06 PM	Rate (0)
Rodrigo F. Experienced Member Joined: 11/29/2013 Last visit: 5/21/2024 Posts: 98 Rating: (3)	Hi Daniel, Thank you for your reply! So, as I suspected, there is no easy way to do DP/PA conversion at the slave side, correct? I am aware of the Profihub modules, but I have a rather particular situation here, in that the networks run through radioactive areas so I cannot have any non radiation hardened active electronics permanently installed on site :) The slaves themselves (the S7-1200/300/200 PLCs) are mobile equipment that is only installed and connected to the network during technical stops, but the network infrastructure is fixed and must remain installed at all times, as interventions are often short and we wouldn't have the time to reinstall the network infrastructure every time. Regarding speed, my networks are already all configured at 187,5kbps, as they do extend almost up to a Km in each segment :) Thanks anyway! Rodrigo
	Last edited by: Rodrigo F. at: 02/03/2022 12:08:35
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2/3/2022 5:40 PM	Rate (0)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 11/11/2024 Posts: 12293 Rating: (2691)	Hello Rodrigo; My experience with Profibus up to now made me understand that chaning a Profibus-DP slave ro a PA device required a change of electronics, namely the ASIC chip. I believed different ASIC chips were required for a Profibus-DP and Profibus-PA slave. So it would require changing out the circuit board with the correct ASIC to switch a DP slvae to a PA device. Now however I have found that Procentec (an other manufacturers, such as Siemens) offers a SPCA4 or SPCA4-2 DP/PA Protocol ASIC that can be used to implement either a DP slave or a PA device. Note that the microcontroller attached to the ASIC shold be programmed according to the protocol selected, so it would require extensive reprogramming, and would still not be an easy task to transform a DP slave into a PA device. "It has to be operated with a processor and heavy protocol software." https://www.profibus.com/products/product-finder/spc4-dppa-protocol-asic Regards, Danieel Chartier
	Last edited by: dchartier at: 02/03/2022 17:42:47 Last edited by: dchartier at: 02/03/2022 19:12:41 Last edited by: dchartier at: 02/04/2022 15:52:45
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This contribution was helpful to 1 thankful Users Rodrigo F.

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