The robot controller supports Modbus over Ethernet (Modbus TCP). The Modbus interface is a widely used communication protocol in the automation industry today, often used when PLCs need to communicate with peripherals like sensors, actuators and instrumentation.
The robot comes with capabilities for a Modbus Server (Slave) as well as a Modbus Client (Master). By definition Modbus RTU uses the terms Master-Slave, in Modbus TCP/IP however, these terms translate to the Client–Server model. A Modbus Server is called a Slave and a Modbus Client is called a Master.
The Server is always running on the robot and your equipment can access the Server at any time to read and write values. This is mainly used when a PLC is present within your application. The Modbus Client functionality, however, is mainly used when no PLC is present, and you want to access a Modbus Device such as a Modbus IO Block to expand the IO capabilities of the robot
This functionality can be used to read the state the UR is in, for example, its current Position, Velocity, and variables that are mapped to registers. Furthermore, you can write to the Robot’s registers via Modbus. This setup enables industrial application as it ensures that your equipment can exchange values with the robot. A typical use case might be to implement a sequencer via exchanging integer values. Depending on the incoming integer value from the PLC the robot executes different parts of the robot program by utilizing the switch-case functionality. On completion, the robot might set a different register to a confirmation number, so the PLC knows that the robot has finished its operation successfully and different parts of the application can continue working, for example a CNC might close the door and start running.
In contrast to the Modbus Server, the Client functionality enables the robot to actively start communication with another device that has a Modbus Server running. One of the most common devices that you might want to connect that way is Modbus I/O blocks. These are I/O Blocks very similar to those of the UR, that enable you to integrate even more equipment by electrical interfacing. Via the Client, it is possible to establish a connection to the I/O Block and Set or Read the states of the various I/O.