I have one device that can only be configured as a Modbus master and one device that for plant reasons cannot be changed to a slave. I now need to connect the two devices and allow one to poll the other. Is there a bridge that will do this? Or a virtual slave that can bridge the two? Thanks.

 

There may be various different hardware or software solutions out there, but since you can't have 2 masters on the same subnet, you'd probably have to have a shared database on a device or PC that that act as 2 slaves on 2 separate subnets, and then the 2 masters can read from/write to this shared database to exchange information at will.

We have 2 gateway devices that will do this:
1. The serial-based XLTR-200, which has 2 RS485 ports and an RS232 port, all of which can be simultaneously configured as master or slave ports, and
2. The ethernet-based ETH-200, which has the same features as the XLTR-200 but also supports Modbus TCP.

If you are interested, please take a look at http://www.iccdesigns.com.

Darrin

 

MatrikonOPC has a Modbus OPC Server that can act as a virtual Modbus slave. This will allow communications between your Modbus masters.
http://matrikonopc.com/opc-drivers/1603/index.aspx

Note that there is no way to have them poll each other, because Modbus masters cannot be "polled".

 

Red Lion's Data Station Plus (DS+) makes a DIN rail mount comm module that is very configurable.

If I understood the Red Lion guy correctly, when I asked about doing exactly this at an trade show recently, it appears that the DS+ can be configured as a Modbus slave at each of two ports, but can be mapped to swap data between registers of each port.

To have Master 1 write a value to Master 2 would involve:
- Master 1 writes a value to port A,
- DS+ moves value to port B at register 40101 (arbitrary example).
- Master 2 reads the value from port B at 40101

If you try it, please provide some feedback as to whether it really works.

David

 

Hi Todd,

HMS Industrial Networks makes a product called the Anybus X-gateway that will function as a Modbus RTU slave on each network and bridge the data between the two.

The product can be viewed on the website http://www.anybus.com.

If you have any questions I can be reached via e-mail at [email protected] or by phone at (312) 829-0663.

Best Regards,
Jason L. Block
HMS Industrial Networks, Inc.

 

Have a look at our Omnii-Comm product http://www.miille.com/din266-p00.pdf
that could be used for this application. It would be configured, for this application, to read in data that is to be shared from each device and place it into a common "database" that can then be accessed from BOTH masters. This would work as a "virtual slave" as I understand your application.

You cannot, at least in the Modbus specification, allow more than one Modbus Master device on a single network.

Please contact me for more information. [email protected]

Jerry Miille
Miille Applied Research Co., Inc.
http://www.miille.com/

 

I talked extensively to a Rep on this device and I also believe that it would work. If I do a proof I will attempt to follow up with a post.