MX615R, MX616R, MX630R, MX648R , ..

8-pin connector according to NEM652 (or "medium interface" according to NMRA 9.1.1) on 70 mm long strands.

MX615F, MX617F, MX630F, MX645F ...

6-pin connector according to NEM651 (or "small interface" according to NMRA 9.1.1) 70 mm long strands.

"21MTC" or just "MTC", based on a 22-pin pin header on the locomotive board and a 22-pin header on the decoder, goes back to an old definition of the Märklin company for the formerly favored "C-sine motors" (electrically commutated motors). The original version therefore contained 3 pins for Hall sensors and a total of 3 pins (instead of 2) as motor outputs. These later superfluous (a total of 4 pins) were used elsewhere after the C-sine era; but in different ways, which is why there are different interpretations of this interface.

Table below: on the far right the NMRA standard valid until about 2016 (where the "C-sine pins" are officially unused - NC), to the left of it the VHDM standard (Railcommunity) adopted in 2016, where these pins are assigned.

ZIMO started using these pins some time ago; currently (2018) there are 4 interpretations, some with switching options; The latest variants - the high-power types MX636D and -C - can be produced in compatibility with the current VHDM standard, as well as according to the ZIMO scheme such as MX634.

Green font in the table indicates possible additions or deviations of the ZIMO decoders to the standard.

There are no differences between ZIMO and standard for the most important connections, i.e. for rail, motor, positive pole, light-front and light-rear functions as well as FA1, FA2 (called AUX1 and AUX2 in the standard).

For the FA3, FA4 outputs, ZIMO offers the option of standard-compliant logic level outputs (C-types) or ZIMO-proprietary amplified outputs ("open collector" such as FA1, FA2, ..., D-types).

The outputs FA5, FA6 are not arranged according to the standard in ZIMO; only the MX636 can be produced in such a Veariante if required.

The direct connection for an external energy storage unit is a ZIMO special feature, with MX634, MX638, MX644 and successors there is a connection for the negative pole of a capacitor (positive pole is set to "Commmon positive", at least 25 V); in the - modern - MX636, on the other hand, a connection for the positive pole of a condenser (whose negative terminal is to be connected to GND, 16 V dielectric strength is sufficient).