Sounds good Mike 
I’m not familiar with the GS20 VFD so it’s good that you’re scrubbing up on this stuff now while you wait for machine delivery. To your questions:
- The pin out on the RJ11 you can find here Technical Manual - SuperLongBoard
- Be aware that the GS20 profile isn’t currently supported in our firmware so you won’t get 1-click setup for it. All this means is that you’ll need to read your VFD manual to find the registers for Run/Stop, Set Frequency, Get Frequency, and the commands for Run CW, Run CCW, Stop, and then after that might just need to tweak the input and output multipliers/dividers once you receive and set up your machine. In the future we might be able to expand to support the GS20 if others are using it too.
- Regarding adapting the existing hookup you use, that may still be able to as well. Many VFDs have a setting to change requiring a 0-10V signal into 0-5V (on the H100 this setting is F070 I believe) so if the GS20 has this option you could try doing this instead. Honestly the reason we stuck with 0-5V was because many VFDs can do this, and those that can’t support RS485, plus we wanted to maintain backwards compatibility to other hobby CNCs and accessories that were build around using 5V
- For RS485 hookup, you shouldn’t need SGND I believe, especially on shorter lengths. If you hookup with 0-5V, then you’d want to use the SGND on the SLB
Hopefully that answers most of your questions!