Let me start by saying I don't have a VFD in my setup, and have never even touched one...
The problem is, VFDs typically can be controlled by a number of methods:
- Digital inputs
- A voltage from 0-5V or 0-10V
- A current from 0-20mA
And with choice, comes confusion.
If it was mine, I'd try to use an RS485 connection, since that's the most direct & feature rich interface. Problem is, it's not the "simplest" way - you'll need a PC to RS485 converter - and then deal with the software aspect (MACH3 configuration, etc).
I'm no expert, but it seems like a fulled feature & suitable unit.