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Accessing MODBUS RTU device through gateway from MODBUS TCP in S7-1200

Created by: jluis.donoro at: 2/14/2012 4:14 PM (9 Replies)

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2/14/2012 4:14 PM	Rate (0)
jluis.donoro Member Joined: 11/26/2008 Last visit: 2/17/2012 Posts: 2 Rating: (0)	Hello everybody, I have a question. Are we able to access to a MODBUS RTU (RS485) device from a controller S7-1200 using the PROFINET interface via MODBUS TCP-RTU gateway? You can see the architecture attached. It would be a great idea to implement a library. Regards. Attachment MODBUS.pdf (1393 Downloads)

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2/16/2012 11:44 AM	Rate (0)
MrPaiva Silver Member Joined: 6/29/2010 Last visit: 10/27/2022 Posts: 112 Rating: (63)	Hello jluis.donoro, You don't need a dedicated gateway for this, you can use a CM 1241 RS485and modbus rtu blocks from the standard libraryon the TIA Portal V11. The CPUwill bethe gatetway in this case.

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2/16/2012 12:25 PM	Rate (0)
smiffy Platinum Expert Joined: 1/17/2007 Last visit: 10/21/2024 Posts: 1547 Rating: (537)	If you do want to go this route, then you can use an external Modbus TCP to Modbus RTU convertor. The one I have used in the past is the XPress-DR-IAP device from Lantronix. This is very easy to setup and works well. You will need the IAP version as that is the only one that supports loadable drivers (you will need to load in the modbus driver firmware which is available free of charge from the Lantronix website).
	Programming today is the race between software engineers building bigger and better idiot proof programs, and the universe producing bigger and better idiots. So far, the universe is winning...
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2/16/2012 3:13 PM	Rate (1)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 11/7/2024 Posts: 3026 Rating: (1056)	jluis.donoro Are we able to access to a MODBUS RTU (RS485) device from a controller S7-1200 using the PROFINET interface via MODBUS TCP-RTU gateway? The answer is In principal yes, but the question is what Modbus on TCP/IP driverblock you intend to use in the S7-1200? The one I know if is available free of charge at Data Communication via Modbus/TCP with S7-1200 (CE-X22). I haven't used this one myself yet though, you will need to be aware of the following: Modbus on TCP/IP adds the so called "MBAP header" (MODBUS Application Protocol header) to the standard original Modbus message frame (you can download the Modbus spec at www.modbus.orgfor more on this). This header contains a so called "Unit Identifier" value. This value exist solely for the purpose of containing theModbus Slave address for Modbus serial devices that are located behind a Modbus TCP to Serial gateway. You will as such need to beable to stipulate this"Unit Identifier" value when you send outout your Modbus TCP/IP message, otherwise the TCP to serial Gateway will not know what to do with the message (well,it could put it on the Modbus serial line, but without a Slave address in it, noneof the Modbus serial devices will want to have it). I unfortunately can NOT tell you if the above linked Siemens Modbus TCP/IP driverBlock does allow to nominate the "Unit Identifier" when assembling the Modbus message (whose value is irrelevant if you communciate in a "pure" Modbus TCP/IP enviroment, so it may have been omitted from the Blocks configuration functionality). Perhaps someone else has the answer to this, if not I suggest you contact Siemens directly and let us know the answer. I hope this helps
	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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6/1/2012 2:47 PM	Rate (1)
Kaulquappe Posts: 3093 Rating: (323)	fritz You will as such need to beable to stipulate this"Unit Identifier" value when you send outout your Modbus TCP/IP message, otherwise the TCP to serial Gateway will not know what to do with the message (well,it could put it on the Modbus serial line, but without a Slave address in it, noneof the Modbus serial devices will want to have it). I unfortunately can NOT tell you if the above linked Siemens Modbus TCP/IP driverBlock does allow to nominate the "Unit Identifier" when assembling the Modbus message (whose value is irrelevant if you communciate in a "pure" Modbus TCP/IP enviroment, so it may have been omitted from the Blocks configuration functionality). Perhaps someone else has the answer to this, if not I suggest you contact Siemens directly and let us know the answer. It is possible to set the unit identifier. See table 12-52 in the S7-1200 manual. Regards, Kaulquappe
Kaulquappe Posts: 3093 Rating: (323)
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This contribution was helpful to 2 thankful Users fritz Seba_D.

8/23/2012 8:37 AM	Rate (1)
ExigoMCL Posts: 6 Rating: (2)	Thanks guys for the tips. I have just tried this with a Scheider PowerLogic EGX300 gateway, and it does work by writing the RTU slave address to "MB_CLIENT_DB".MB_UNIT_ID
ExigoMCL Posts: 6 Rating: (2)	Last edited by: ExigoMCL at: 8/23/2012 8:46 AM
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This contribution was helpful to 1 thankful Users fritz

6/10/2013 5:45 PM	Rate (0)
leningfe Posts: 2 Rating: (0)	Hi, I am sorry if this is too late. But you could have used Sentron Pac 4200 as a gateway. It needs the RS485 accessory. Check its manual, un der descriptions-->gateway. https://support.automation.siemens.com/WW/llisapi.dll?func=cslib.csinfo&lang=es&objid=7KM4212-0BA00-3AA0&caller=view Regards Lenin
leningfe Posts: 2 Rating: (0)
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5/1/2017 8:49 PM	Rate (0)
GiacomoIT Advanced Member Joined: 10/19/2012 Last visit: 6/8/2024 Posts: 1 Rating: (0)	Kaulquappe fritz You will as such need to beable to stipulate this"Unit Identifier" value when you send outout your Modbus TCP/IP message, otherwise the TCP to serial Gateway will not know what to do with the message (well,it could put it on the Modbus serial line, but without a Slave address in it, noneof the Modbus serial devices will want to have it). I unfortunately can NOT tell you if the above linked Siemens Modbus TCP/IP driverBlock does allow to nominate the "Unit Identifier" when assembling the Modbus message (whose value is irrelevant if you communciate in a "pure" Modbus TCP/IP enviroment, so it may have been omitted from the Blocks configuration functionality). Perhaps someone else has the answer to this, if not I suggest you contact Siemens directly and let us know the answer. It is possible to set the unit identifier. See table 12-52 in the S7-1200 manual. Regards, Kaulquappe You are the best! ;)

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10/28/2019 4:27 AM	Rate (0)
daica2 Member Joined: 12/12/2018 Last visit: 3/5/2023 Posts: 2 Rating: (0)	can you share some information Accessing MODBUS RTU device through gateway from MODBUS TCP in S7-1200 to me. thanks
	van minh
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10/29/2019 3:12 PM	Rate (0)
Duris_I Diamond Expert Joined: 4/28/2015 Last visit: 10/30/2024 Posts: 10585 Rating: (825)	Hello, hope you ask all users for help, or specific one? From your question is not clear to me, sry. Generally, you don't need ask for specific procedure because on Client side (MB TCP) you just use MB TCP system for exchange data, nothing special. One important option is Unit_ID which in this case set RTU Slave address if you need, simply in case of Gateway and RTU on other side is important set correctly. Gateway make conversion business internally from MB_TCP to MB_RTU, you don't need do nothing with conversion.
	With best regards... Ivan Duris Flight: OMICO
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