ModbusRTU Data Concentrator


Thread Starter

Lucas Williams

I am looking for a device with the following specifications.

2 rs232 ports to function as ModbusRTU masters.
2 rs232 ports to function as ModbusRTU slaves.

The two master ports should poll independently of each other but allow a shared memory space inside the controller.

The two slave ports should be able to respond independently to ModbusRTU queries drawing from the shared memory space to provide valid responses.

Does anyone know of such a device? Thanks for your help.
Option 1: Modicon PLC w/ a BM85 Modbus Plus to 4 Modbus Ports Bridge/Multiplexer. Controller holds up to 10K of data, MB+ gives master cababilty.

Option 2: PC w/ 4 COM ports w/ a Visual Basic App. Gives PC ability to act as Master and/or Slave.

Eric M. Klintworth

You could do this with an Allen-Bradley SLC-5/03 and two Prosoft 3150-MCM Modbus modules. The modules have two ports each separately configurable master or slave. Prosoft info is at
<> If you have a huge amount of data the SLC-5/04 or /05 have more memory than the /03.

Eric M. Klintworth, PE
Columbus, Ohio

Ernest Whitehead

Try Bristol Babcock or Dexter Fortson Associates ( 1-205-491-8665) These two companies could help you

Greg Meister

Mr. Williams:

The 8051 Communications Bridge from Sierra Monitor will do what you require. It has a total of eight RS-232 ports, two RS-485 ports, two
independant 10BaseT ethernet ports and an ISA-bus slot for other communications cards. It supports Modbus, Modbus/TCP and many other protocols, so it does what you need as more. You can find it at

Greg Meister
NAC Northern Automation Controls Inc.
Email: [email protected]