furthermore it affetcs also the volume of the vst plugin in cubase.
For example. I am using a Clavinet sound in Halion. I right-click on cutoff and say "Learn CC", I move the pedal and it learns to change the cutoff with the pedal.
But still it's changin also the volume of the instrument

In order to change your ASSIGNABLE FOOT CONTROLLER jack from FC1 to FC2, you must change it to the same cc number as FC2.

Go to [UTILITY] make FC1 = cc04 Foot Control
Press [F4] CTRL ASN
Press [SF1] ASSIGN
Make FC1 = 04[Foot Control]
and leave FC2 = 04[Foot Control]

Can you tell me exactly which is the difference between FC1 and FC2.
From the manual I understand that FC2 referx to an external midi instrument, so, if I am using only my MOXF I can ingore it, right and put it to off, right?

Can you tell me exactly which is the difference between FC1 and FC2.

Yes. It's a little complicated but here goes. The MOXF is the Motif XF engine with some modifications. The internal tone generators are identical, some of the physical input and output options are different. The bigger brother engine allows for two FC7 sweep type Foot Controller pedals, two momentary Foot Switches one dedicated for sustain, the other assignable, it has a Ribbon Controller, two Assignable knobs, two Assignable Switches, a MW, a PB Wheel, and even Breath Control.

Now, even though the MOXF doesn't have a physical Ribbon, nor a second Foot Controller jack, and neither the MOXF nor the Motif XF have a Breath Controller jack, it does not mean that they cannot be programmed to respond to these devices.

Here's how that works. The MOXF has but one physical FOOT CONTROLLER jack. By default, it has been designated FC1. You can, however, switch its function to be FC2.

The reason two Foot Controller devices are provided on the bigger synth engine, is because one is typically used for Expression (relative musical volume), while the other, FC2, is left without a fixed function _ allowing the user to program it (assign it) on a per Voice basis. Making it a wah-wah pedal for a guitar, or second discreet volume pedal when wishing to control two separate sounds each w/pedals, or to pan something across the stereo field, switching LFO speed on a Rotary Speaker effect, or a score of other things as the particular Voice might require. Each on a case-by-case basis.

That's the difference between cc011 Expression which always affects volume. And cc004 Foot Control which is assignable to, literally, any one of 100 possible Destinations. So you have a "fixed" and an "assignable" sweep pedal option.

The MOXF only has the one jack, so you must choose which do you want: a pedal that always does volume (Expression) or one that can be / must be programmed within the Voice.
By default, you discover that
FC1 = cc11 Expression
FC2 = cc04 Foot Control

By going into Controller Assign and making FC1 = cc004, it affectively becomes FC2
Now within the CONTROL SET when you set the SOURCE = FC2(04) the selected parameter will respond.

Hope that helps.

If you encounter a Motif XF Voice that has something assigned to the Ribbon Controller (22), the MOXF does not have a physical Ribbon, but by setting FC1 = cc22 it will affectively become a Ribbon (or at least change the parameter that was originally programmed to the XF's Ribbon).