Hello everyone.

For a student project I'am trying to add a non extrusion tool to a multitool 3D-printer.
To be pricise the new tool is a dispenser, to apply soldering paste.
RepRap 3.3 (I know, out of date) on Duex5 v0.11

I stumbled apon M571 and tryed to get it to work via an unused FAN output and GPIO.
The lines are:

M571 P"duex.fan8" S1.0
M571 P"duex.gp1" S1.0

None of these commands work how they should. Nothing happens and no error massage. However GPIO will switch on the signal, as soon as it hits the M571 line.
What am I missing?