Hi,

I am trying to get a higher speed communications between two different DCSs (Delta V & Moore APACS). Moore is limited to Profibus, Modbus, and OPC interface for communications. Delta V has multiple platforms of communications. We do not want to use an OPC interface because of inherent fault due to a PC. Modbus is limited in speed to 19.2kbps. So with limited experience in Field Bus we figured the PROFIBUS with speeds up to 14Mps would be just the ticket.

Wrong assumption on our part. Both the Moore APACS and Delta V DCSs Profibus interface is PROFIBUS DP and both units must be a master unit.

My question is can MASTER to MASTER communictions be accomplished on a MULTI-MASTER Proifbus node without any slave devices.

Has anyone attempted doing the above? Can master to master comms over Profibus DP be accomplished?What hardware issues and software/programming issues did you run into?

Regards
Mark

 

Hello, Mark;

You cannot exchange data directly between 2 Profibus-DP masters.

The easy way to transmit data between Profibus-DP masters is to insert on the bus a special slave called a DP/DP coupler. This slave has the peculiarity of having 2 distinct Profibus-DP slave interfaces. So it can be seen as a slave by each master; each master can read/write data (up to 244 bytes per exchange) to its slave, and the Dp/DP coupler acts as a bridge between the 2 masters.

Follow the following link for a descriptive manual on the coupler:

http://www4.ad.siemens.de/dnl/zMzODM1OQAA_1179382/dpdpk_e.pdf

Hope this helps,
Daniel Chartier

 

Solution:
Use a Profibus DP-DP Coupler: (i.e. Siemens 6ES7 158-0AD00-0XA0)

The DP-DP Coupler can be used for joining 2 PROFIBUS networks together, irrespective of whether there is an slaves on the network or not.

How much data can be transferred with 6ES7 158-0AD00-0XA0 DP/DP coupler? 256 bytes inputs and outputs together (i.e. 120 bytes in, 136 bytes out), max. 240 bytes per direction.

Regards,

Jason Whelan

 

You have to use a Profibus DP coupler to connect two Profibus DP masters. As far as I know only Siemens can supply that product.

 

1. Modbus per se is not limited to 19.2 kbit/s. There is no specific limit to Modbus. Many Modbus devices support 115.2 kbit/s and perhaps more. It is a limitation of the hardware interface only. Both Modbus and Profibus use RS485. Is it either one of the interface cards that has this limit, if not you can go faster? It may be worthwhile checking one more time.

2. What about Modbus/TCP, i.e. Modbus over Ethernet? Many devices that support Modbus/RTU also support Modbus/TCP.

3. You can talk Profibus-DP master-to-master using a DP-DP coupler. Not sure how to set it up in your case though. The control systems may not support configuration of such a coupler so you may need a separate configuration tool.

Jonas Berge
SMAR
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[email protected]
http://www.smar.com
Learn Fieldbus at your own pace: http://www.isa.org/fieldbuses

 

Hi,

Of course you can exchange data between two Profibus-Master direct!
I don't know your devices but connecting two S7 plcs via Profibus Master is easily to configure in Step7.

I would recommend the DP/DP coupler just for couppling two stand allone facilities which has already Profibus networks running - so you have less implementation effort.

If you need to implement Profibus into the machine just for this communication problem - let them talk directly to each other.

Hope that helps

Best regards,
Konni (Konni(at)Kon-Tech.de)

 

Hello,

Thanks guys appreciate the help.

Mark