I am thinking of using mgate mb 3180 modbus gateway to connect multilple modbus tcp slaves with multiple rtu masters. Different master will poll different slave. We have only one serial and one ethernet port on the Modbus gateway. How can we connect multiple slaves and rtu masters through same gateway?

Thank you!

 

You can't. Modbus RTU can only have one master per RS-485 bus. You would need to use the 2-port 3280 or the 4-port 3480. Another option would be to use one 3180 per Modbus RTU master.

 

You can't. Modbus RTU can only have one master per RS-485 bus. You would need to use the 2-port 3280 or the 4-port 3480. Another option would be to use one 3180 per Modbus RTU master.

Thank you!!

 

I have a simmilar issue. I need the slave devices (rtu) to connecto simultaneously to 2 masters (either rtu or tcp). Which device can manage this?

 

For serial-based Modbus (e.g. Modbus RTU or Modbus ASCII), there can only be one master on the RS-485 bus. However, for Ethernet-based Modbus, you can actually have multiple clients (i.e. masters) communicate to a single server (i.e. slave). The number of simultaneous clients allowed depends on the limits set by the manufacturer of the server device.

There are two types of devices that will allow you to perform conversion between Modbus/TCP and Modbus RTU.

1. A Modbus Gateway
   1. A gateway device requires the user to configure register mappings for all Modbus registers that will be accessed through the gateway. The registers from each port are typically mapped to an internal database on the gateway.
   2. Both ports communicate independently from one another and requests are responded to immediately using the data from the gateway's internal database.
   3. A gateway allows remapping, or changing, the register definitions and can be used to emulate other Modbus devices.
   4. An example of a Modbus gateway is the ICC ETH-1000.
2. A Modbus Router
   1. These devices require minimal configuration and simply repackage the Modbus messages from one encapsulation to the other.
   2. Routers introduce a small delay in the messages, as it takes time for the router to receive the message, de-encapsulate it, re-encapsulate it, then send the message.
   3. An example of a Modbus router is the Moxa MB3180 (note that this device actually supports both router and gateway functionality).