@dc42
Thank you so much!
For the first time I feel I have understanding of the revised gcode and post processor and therefore full control of my laser - really only now for the first time.
Tomorrow will be busy. Thanks again

@dc42
I have to be able to adjust the focus of the laser onto the surface - may be different heights depending on job - (turn it to low power and adjust Z height), before starting to etch a design on low power or cut through.

With the cutting, as it is only a 10 watt diode, it relies on a critical focus to cut, I have heard that I should move the z down slightly during a multiple pass cut to achieve the most accurate cut. Will I have to do this manually?
I'll try out the new pp now and report back, if I may.

@dc42
done some digging - ascii codes to replace the quote marks.
Putting it all together, have I understood it correctly please:...

• ######## RepRap 3 NEW COMMANDS #########
  +---------------------------------------------------
• Command output after the header to switch LASER on
  +---------------------------------------------------
  +======================================================
• CLEAR FAN PIN OUTPUT BUFFER
• release DUET pins 'fan 2' from FAN output
  "M950 f2 c[34]nil[34]"
• DOUBLE CHECK: RELEASE MAPPED GPIO OUTPUT P4
  "M950 P4 C[34]NIL[34]"
• PREPARE GPIO output 'p4' ONTO FAN2 PINS AT 50HZ
  "M950 P4 C[34]Fan2[34] Q50"
• ====================================================================
• switch to LASER MODE on fan 2 logical pin 4, 20/255ths power @50Hz
  "M452 C[34]fan2[34] r20 Q50"
• ====================================================================
  "G0 [XH] [YH]"
• Rapid Home x&y axis

•   "G0 [ZH]"
  

• Rapid Home z axis

• commented out to prevent z movement #### WORKING

+---------------------------------------------------

• Commands output for rapid moves
  +---------------------------------------------------
  begin RAPID_MOVE
  "G0 [X] [Y] [Z]"
  +---------------------------------------------------
• Commands output for the first feed rate move
  +---------------------------------------------------
  begin FIRST_FEED_MOVE
• ####### RepRap 3 NEW COMMAND #########
  "M42 P4 S0.5"

•  Switch i/o pin P4 to 50% 
  

• ########## END RepRap 3 NEW COMMAND #######

Syntax query for the new M452 - was originally embedding it in Vectric post processor to automatically switch to laser mode. Ie "M452 P2 R50 F500" (Quotes are expected).
New M452 ie: "M452 C"fan2" R50 F500" errors because of the two sets of quotes I assume. Any thoughts as to a work around?

@dc42
'gpio port has no pin' - so why has the m950 p4 line not mapped onto fan2?

@dc42
Been trying for the last hour or so, briefly got it responding, but would give me output in laser mode using M42 without the m452 command?

Stubbornly refuses to release in either laser mode or cnc mode.
So put this macro together to try... if I am missing something, I apologise, but the comments are how I understand the logic... still not releasing!

; RRF3 fan ON test
;################### HALF POWER AT 50HZ ##################

; SET CNC MODE
M453

;======================================================
; CLEAR FAN PIN OUTPUT BUFFER
;======================================================

; release DUET pins 'fan 2' from FAN output
m950 f2 c"nil"

; DOUBLE CHECK: RELEASE MAPPED GPIO OUTPUT P4
M950 P4 C"NIL"

; PREPARE GPIOO output 'p4' ONTO FAN2 PINS AT 50HZ
m950 p4 c"fan2" Q50

; SWITCH output ON p4 at HALF power 125/255
m42 p4 s125

@dc42 Ok - Can use a macro to laser engrave after setting up first in cnc mode.
Will still need to send output to Fan 2 - how can I release the pins for output if NOT in M452 mode (nil doesn't work)

@woodworksimon
Re the output from Fan2, (when we get it working) is it available to manually control as intended from a macro when stationery? BTW, am getting a steady 0.2v across the heater pins - correct?

As I am double handling the CNC, I call the laser with a macro and return it (for safety) to cnc from the macro when when finished. The above settings were made in cnc mode (M453) and the m452 was only called after the M950 line.
If I run P4 C"nil" does that not release the pin anyway?

@dc42
1: Fan 2 (left hand pwm fan output on board) working before upgrade.
2: M950 P4 C"fan2" gives: Pin Fan2 is not free, so sent P4 C"Nil" , but still not free.
3: M452 is set to c"fan2" Q2000, and I have also prefixed the lines in my macro with M950 P4 C"nil" and M950 P4 c"fan2" to double check.