Modbus Master-to-Master Communication

Control systems on each structure were configured to communicate with each other through a serial Modbus RTU RS-232 or RS-485 channel. However, the Modbus device configuration on each side was designed to communicate as a master, while traditional Modbus communication takes place between a master and a slave.

Each structure''s respective developers had invested substantial resources into their control systems, so the systems integrator needed to find a way to overcome this obstacle by converting one configuration to act as a slave in the most cost-effective way possible – or by making two Modbus master devices communicate with one another. Many industry experts have expressed that master-to-master Modbus communication is impossible, but Comtrol had already developed an innovative solution to allow a Modbus master communicate with another master.

The systems integrator assigned to this task researched master-to-master connectivity and ultimately discovered the DeviceMaster UP''s capabilities on a respected online forum. Hesitantly beginning the application, the integrator was highly satisfied with the end result.

As seen in the diagram, Comtrol was able to fix this integrator''s problem using the DeviceMaster UP 2-Port 2E Modbus gateway. By running Modbus Router firmware, an internal slave that resides in RAM is provided that responds to commands from any properly connected external Master. The Modbus Router firmware was developed to provide innovative network-wide Modbus connectivity from a wide variety of Modbus masters to a wide variety of local and remote Modbus slaves. Advanced features include the above-described master-to-master communication and also private serial bus connectivity, write protection, and device ID aliasing. With simplified configuration pages and advanced routing, Modbus Router provides unmatched Modbus connectivity.