I¡¯ve never seen documentation of the ECoS protocol.
I believe you will find that it is the same as the protocol for the original Marklin central station, as ESU made that for Marklin, then came out with their own unit, which shared many features with the Marklin one. I provided a google translation of the original Marklin documentation which allowed the JMRI team to get the original connection to the Marklin cs1 done, and I believe that was then expanded to the ESU unit.
