Mesa 7i96 PWM for 0-10v VFD spindle

I'm gradually solving a series of problems with setting up my 3 axis mill thanks to everyone's help. I now want to get the spindle speed control working properly. Its been working of sorts but it has only been coming on when i reach 50% of full speed. Im using PWM on stepgen 4 and 2 SSRs to switch on and ccw. The SSRs work fine. Its a generic chinese AT1 VFD. Its complicated by needing a filter to smooth out the PWM as without it the rpm was fluctuating (as suggested by PWC and it seems to work). I had been running the input at 0-5v, but I'm trying to switch to 0-10v as that is what everything i read seems to talk about. I've worked out you to change P075 on the VFD to take a 10v input as opposed to 5v, but don't know how to wire it to the 7i96's PWM (on stepgen4).

1. I think I need to take the difference between step+ (+5v) and step- (-5v) to get the 10v, is this right?

2. If the above is correct, do I put my filter between step + and step -, as if step- is gnd/0v and step+ is positive?

3. I wire (the filtered) step+ into VLi on the VFD (this works fine with a pot)

4. What do I wire into common on the VFD? Step- ? Or Gnd from the 7i96? I assume the former or I won't see a potential difference of 10v? As such I'm not connecting gnd between the 7i96 and VFD at all?

No, you cannot ground STEP- or DIR- outputs, will short out the 7I96 outputs and possible damage the 7I96, Best you can get is 0 to 5V from a step output.

Can you scale the VFD frequency settings so you get full scale RPM from 5V?

You can get 0 to 10V by using a SSR output with software PWM but the PWM frequency has to be quite low (say 20 Hz) so you need a long time constant filter

Thanks for the quick reply Pete. So I simply wire step+ (from stepgen4) into Vli and gnd from the 7i96 to common on the VFD? I leave the VFD config as default (0-5v). I put my filter between step+ and gnd/common?

Step+ would go into the R part of the filter:

Step+ --> R.1
R.2 --> C.1 --> VFD VIN
GND --> C.2 --> VFD Analog Common

R.1 means R pin1 etc

I can happily report this is now working, thank you. I can move onto my next issues, the estop .and testing the glass scale linear encoders. New threads for those.