Connecting multiple masters to one slave


Thread Starter


Emerson mass flow meter connected to Rockwell PLC over MODBUS RTU in read write functionality.

Now we need to share the same data using the same RS485 port for monitoring in Honeywell HPM using SI interface.

Is it possible to use splitter or a bridge to share the same port?
What will happen if both masters ask for data at same time? Will the data gets affected in concurrent operation? Only read function is expected in Honeywell master.

Yes it can be done using a gateway, still use Modbus RTU to the mass flow meters, possibly use EtherNet/IP to Rockwell, then Modbus TCP/IP or something else to connect to Honeywell, can does this fairly easily.


Jerry Miille

You will need a "message scheduler" product to do this. It will need to monitor both Modbus Master requests and co-ordinate the requests to the slave so that they do not interfere with each other.

There are products on the market that provide this connection. We sell one that we call a "Multii-Port" that will provide this capability.

You can find us on the internet by doing a search or clicking on the link above.

Jerry Miille

Darrin Hansen

If you're looking for the lowest-cost solution, I'd suggest the ICC XLTR-1000 gateway ( It's a 2-port RS-485 device, and supports Modbus master, slave and sniffer drivers. The sniffer driver is non-invasive and can be installed on any existing Modbus RTU network: it pulls the data off the network and exposes it to the other port on the gateway (which would typically then be running a standard Modbus RTU slave driver). It's commonly used in scenarios where you need to read data from an existing master/slave network with another master.


Thanks for your reply but we use Honeywell TDC3000 in which serial interface supports MODBUS RTU/ASCII only and not MODBUS TCP