Hello\

I need Siemens modbus RS 485 repeater, this will work ? it say profibus not modbus

6ES7972-0AA02-0XA0

https://mall.industry.siemens.com/mall/en/uk/Catalog/Product/6ES7972-0AA02-0XA0

if not work, can you please recommend Mosbus RS 485 repeater from other company?

Thanks to you

Hello Asimo,

but this type already recommended to you mr. William_B in other topic, also other types. Do you have any other problem with selection?

 Hello, thanks for reply

I have doubt becuse it only has profibus cable not terminals, manual does not say how to connect the 3 wires, and the ports of device only profibus, how can I use it for modbus?

Duris_I

Hello Asimo,

but this type already recommended to you mr. William_B in other topic, also other types. Do you have any other problem with selection?

 I meant 3 wires as in A, B and GND, I thought it is only profibus rs 485 repeater not modbus when I saw the profibus port, and it says in product description "SIMATIC DP, RS485 REPEATER FOR THE CONNECTION OF PROFIBUS/MPI BUS SYSTEMS" so that means it is not modbus rs 485 only profibus/mpi , no ?

I am trying to understand here, why do every expert here think everyone is expert like him? I am asking for help only.

Marko Bursic

Which 3 wires? Modbus has A,B wires like all RS485 devices. What terminals? It's a repeater: a cable comes in and the cable goes out. It has screw contacts, you put in the wire and secure it. The accessible port DB9 is profibus standard connector for manteinance access - it's the same cable routed on the DB9 connector, if you don't like it you can leave it.
What are your expectations anyway? How do you imagine a RS485 repeater? 

ASIMO99

I am trying to understand here, why do every expert here think everyone is expert like him? I am asking for help only.

Hi Asimo99,

I am very sorry if my previous answer in your previous question was not helpful to you. I would not have been offended if you told me so.

Sadly it is very probable the people that is worth calling 'expert' may not even contribute on this post... I am not worth calling an expert.

---

For your case Modbus RTU share with Profibus / MPI  the same type of hardware configuration - RS485. The "language" (protocol) spoken by each of those look different, but the medium stays the same.

The repeater is not a protocol converter. It does not matter what protocol is repeated, only the voltages received and re-transmitted. Be careful for not getting a diagnostic capable repeater - this may cause issues.

Modbus RTU do not need the earth wire to be able to communicate. Having the shield linked to the body of the DB9 connector plug is a good idea. I would expect that information to be included in the documentation of the repeater you have in mind to get. The manual found here mention grounding on page 15.

I find no technical reason why you cannot use the Profibus repeater as a Modbus RTU.. but I have no experience to back it up. This fact as well as the pricing that Siemens ask for their equipment, make me still stand on mu suggestion to getting a non-Siemens repeater.

It is not the answer you want, but it is all I can offer. Do consider chatting to an actual sales-engineer.
w

@Others... Anyone out there have experience to share?

Now I fully understand.

Thank you very much William and thank you Marko, for me a logical answer with some description makes you more than experts/teachers.

I really appreciate your help and fast replies on this topic ^_^

Before you buy, look this:http://s7detali.narod.ru/NET/PB_rep.html

The rpeateater has inbuilt MCU, for autobaudrate selection. Now, it could be that at startup, it seeks a specific telegram from Profubus, MPI to set the correct baudrate. Therefore it might not work properly with Modbus. The correct budrate and correct switching TX/RX of the transceiver is indispensabile for proper operation. I would reccomend you to go with different industrial brand like Moxa, Hilscher, Helmholtz,...that has the abiltiy to set the baudrate via dip switches, no autobaudrate.