I could be wrong, I did not delve in to deep, but this looks like it may be a standalone motion controller rather than just a drive unit alone, If so this is used to store moves and simple point to point programs, It may be possible to place it under the direct control of a separate motion controller, but if it is what I think it is, this is not the primary reason for it.
Al
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.