What is this in the Modbus example

[RTSLVU]

I am new to Modbus and downloaded the NI Modbus VI's 

Looking at their example there is a VI who's icon looks like a cube, but this VI is no where to be found on the Master or Slave Modbus API

Undocumented example code is just as bad if not worse than no example code.

[PiDi]

This is an object: https://www.ni.com/docs/en-US/bundle/labview/page/classes-and-objects.html

Create it as constant from wire/terminal.