@jay_s_uk
Many thanks. I will do a few tests using various options.
FYI, my VFD allows me to disable the REV direction (which I have already done to prevent broken end mills!!)
Many thanks again.

@jay_s_uk
v2.03

I have just been looking at using a fan output instead. M106 P2 Snnn.
Would this work?

@jay_s_uk
I do use M453 cnc mode. How do I assign a particular pin as a PWM output?
Would it just be a case of M453 P4 R24000 (max spindle speed) and then M3 S255 for max speed?

I want to add a PWM output from my Duet3D board to control a VFD and spindle.
I have a PWM to voltage (1-10v) board that converts a PWM value into voltage. (5v =50%, 10v=100% etc) that connects to my VFD.

QUESTION:

Can I use heater 4 (on pin 13 of the Duet board) as a PWM output by using the following in my post processor?

M307 H4 A-1 C-1 D-1 -- to disable heater 4
M42 P4 Snnn --to send a PWM value

Not a problem
It would appear that I am on RRF2 as I am using a WorkBee from Ooznest so the velocity ramping is not useable

@dc42 You put "Laser power sticky" in M42 .
That's what threw me

Select "laser power sticky"

How do I do this?

@dc42 Thank you.
My next question is this. The following code moves the laser (CNC) in the defined square but only switches the laser on for the first line (or one side of the square).
M3 S255
G1 Y75.0000 Z0.01000 F2500.0
G1 X75.00000
G1 Y25.00000
G1 X25.00000
M03 S0

If I add an S command to each line it works OK

Is there a way round this?

Do I need to activate this velocity ramping or does it just work as is when in laser mode?