Why is it impossible to mount non-ESU decoders in some L. S. Models products?

This question was asked many times on the forums, whenever a new LSM model appeared, roughly since the release of the BB 16500. Neither the 40100 nor the previously released EADs were affected, as they are equipped with an eight-pin standard interface.

Recall of facts

If you try to mount a decoder other than ESU in a recent LSM machine with a 21-pin interface, the motor control works, but not auxiliary functions (lights, cabin lighting, etc.) This is clearly done to force the consumer to buy an ESU decoder. But how did they do to make this curious operation possible, and frustrating if one is accustomed to another brand of decoder?

Examples of machines concerned

I will just quote the machines I have, but I know there are many others.

The principle

I’m going to explain to you in the following page the principle of the sleight of hand realized by LSM, but I confess that I have not yet solved some questions.