Accessing Robot from ModBus

I am in a classroom situation and need to learn more about how to access our robot from modbus. Specifically I want to get the status of the robot.
Any help is appreciated.

What PLC system are you using?
I communicate MODBUS with my UR from mitsubishi and Click PLC.

The Modbus server document are for signals where the UR is in control. This is how I send the robot status (Address 258) to my PLC systems.

https://www.universal-robots.com/articles/ur/interface-communication/modbus-server/

Then to setup registers and I/O with the robot I use the PLC server functions. and establish the connections under the Installation tab / Fieldbus section.