MX600: the cheapest DCC decoder from ZIMO, also with the lowest height (components on one side only). Despite a price in the range of 20.00 euros, there are only minor limitations compared to other ZIMO decoders: there is no SUSI interface, no servo outputs, a larger starting voltage in analogue mode . CAUTION: The  MX600P12 version, with PluX12 interface, is longer than the PluX 12 standard (25 instead of 20 mm).

MX616: the smallest ZIMO decoder (8 x 8 x 2.2 mm), full functionality like all ZIMO decoders, despite miniaturization. 24 V dielectric strength, 6 "normal" function outputs, but no SUSI pins (therefore no servo control), NEM651 or wired.

MX617 to MX618: Types with larger EEPROM memory for up to 1024 CVs (instead of 256 CVs of the other non-sound decoders) This provides additional features and memory for future storage of GUI data - name, image, FI symbols - for control units.

MX617: Miniature decoder (13 x 9 x 2.5 mm), functionally and connection-wise largely the same as MX616, less extremely miniaturized and therefore (potentially) more robust than this one, 6 "normal" function outputs, but no SUSI pins (therefore no servo control), NEM651 or wired.

MX618: DCC decoder (MM protocol also supported, but rarely of importance) with Next18 Interface (18-pin), according to the "Rail Community" (VHDM) standard RCN-118 for Sizes N and TT; full ZIMO features, including servo control, SUSI, etc.

MX621: (discontinued in 2018)  The ideal DCC decoder for the smallest scales and where this is a lack of space (no MM - Motorola - protocol!) . Despite miniaturization the decoders is largely identical with the larger types (MX622, MX630, ..), but servo-control, SUSI, and  the ZIMO special function mapping are NOT available (for small locos usually not needed anyway).

MX622:  Not quite as small as the MX621, but without the functional limitations of the MX621, similar to larger ZIMO decoders, available either wired or PluX12 (narrow enough for the 12-pin interface).

MX623: Cheaper version of the MX630, derived from the MX630, narrower, less motor and total power, 6 instead of 4 "normal" function outputs; equivalent for many applications to the MX630. In the PluX12 version suitable for all locomotives with this interface because no wider than the plug itself.

MX630:  The "high-volume" ZIMO decoder for 00/H0 scales, wired or PluX16 interface. Generously equipped (6 full-value, with a total of 8 outputs for functions), plenty of memory in reserve for future SW updates (new features added to RailCom),for a standard decoder takes up very little space. 

MX632: (discontinued in 2018) highest power rating in the dimensions of a small scale decoder, otherwise similar to MX631 (wired or 21-pin, external storage interface), and also the low-voltage output (1.5 or 5 V) for functions in the V and W versions.

MX633 to MX638: Types with larger EEPROM memory for up to 1024 CVs (instead of 256 CVs of the other non-sound decoders) This provides additional features and memory for future storage of GUI data - name, image, FI symbols - for control units.

MX633: Fully equipped with function outputs following PluX Standard (9 outputs, by additional use of the index pin 10 outputs), with energy storage circuitry (for 16 V capacitors and Goldcap packs), therefore can also be used as an alternative to PluX16 MX630.

MX634:  The MX634D version is ZIMO standard decoder for the 21-pin interface, in the wired versions similar to the MX630 but with higher capacity, and connections for external energy storage (capacitors) against a bad connection.

MX635: like MX633, thus fully equipped with function outputs, energy storage connection etc., BUT: Semi-synchronous rectifier for higher motor current and total load capacity (up to 1.8 A) and also low voltage source for function outputs in versions V (1.5V) and W (5V)

MX636: like MX634, i.e. 21MTC interface in versions "D" and "C", BUT: energy storage connection also for 16 V electrolytic capacitors and gold caps (same as the PluX types, not like the other MTC types), AND: semi-synchronous rectifier for higher motor current and total load capacity (up to 1.8 A), and also low voltage source for function outputs in versions V (1.5V) and W (5V)

MX637P22: (no wired versions): like MX633P22, i.e. with PluX22, but NO energy storage connection, therefore cheaper and called "Economy High-end Decoder"; most locomotives with PluX22 interface do not have energy storage capacitors built in anyway (this might change in the future)

MX638D, -C: (no wired versions): like MX634D, -C, i.e. with 21MTC, but NO energy storage connection, therefore cheaper and called "Economy High-end Decoder"; most locomotives with PluX22 interface do not have energy storage capacitors built in anyway (but this might change in the future)

MX648: The smallest (subminiature) sound decoder in the ZIMO range, with the dimensions of a standard (NMRA) non-sound decoder (LXB = 20 x 11, so as MX630)!

MX649: The miniature sound decoder with the smallest dimensions in the ZIMO program (23 x 9 x 4 mm); yet fully equipped and voltage up to 30V, suitable for N and TT model, with the "N" type with NEM-651 interface and in the quasi-standard width of 9 mm.

MX645: The "standard model" for 00/H0 sound in the ZIMO decoder range, either wired or PluX16, PluX22, 10 function outputs, and connections for external energy storage, especially important for uninterrupted sound.

MX644D, -C: (no leaded types, since these exist from the functionally identical MX645): Sound decoder for the 21-pin interface, connectors for external energy storage.

MX658N18(no leaded types): DCC sound decoder (MM protocol supported, but rarely of importance) with Next18 Interface (18-pin), according to the "Rail Community" (VHDM) standard RCN-118 for Sizes N and TT; Special version with 22-pin connector available for special vehicles.

MX659N18:(no leaded types): DCC sound decoder, very similar to MX658N18, but smaller (5 mm shorter, 1 mm narrower), therefore internal sound energy memory smaller (more sensitive to voltage interruptions)

The dimensions of the ZIMO decoder in accordance with the NMRA DCC standards (RP 9.1.1) and / or NEM specified values ​​or within the specifications, if there are such standards, and with the specified connectors integrated (where relevant):

- MX622 corresponds to RP 9.1.1 for Decoder with "small interface",
- MX630 corresponds to RP 9.1.1 for Decoder with "PluX16 interface,
- MX630P corresponds to RP 9.1.1 for Decoder with "PluX16 interface,
- MX634D, MX634D, MX640D corresponds to the decoders with "21-pin-connector"
  (in each case, depending on if a sound or non-sound decoder). 

ZIMO decoders and system devices are multi-protocol capable and support various digital and analogue operating modes. The line above indicates this for the respective decoder.

Possible operating modes:

The maximum "continuous current" is the current load of the motor output and the other outputs ("Total"), where average ambient conditions are assumed. Limiting the current results in heating of the decoder, the built-in temperature sensor allows approximately 100° C temperature before deactivation of the decoder, as opposed to "peak power" (see below), which deactivates the decoder when this value of the current is exceeded..

Indication of overload (= over temperature) in the decoder is by flashing headlights in fast mode (5 Hz), the reconnection of the motor happens automatically after cooling down to about 20 °C (hysteresis).

Specifying a maximum continuous current is actually a simplification, although common to all decoder manufacturers, because a really correct specification is enormously extensive and hard to understand. Possible influences on the actual duration of power include:

- The higher the rail voltage, the more heat loss, and lower current for potential power ("normal" for 00/H0 about 16V),
- Type of Motors, low impedance windings produce more load, external energy storage capacitors reduce the loss,
- State of the engine, poor lubrication, of course, increases the load (this is actually due to the increased current),
- Air temperature inside the locomotive, heating metal parts (engine, unfavorable) or cooling metal parts (favourable).

Experience shows that for a "normal" 00/H0 loco (newer design) the 'normal' decoder MX630 is almost always sufficient, even if it is specified as "only" 1.0 amp. For special cases such as frequent driving on multi-level layouts or curved track with long trains, or for older twin-engined vehicles the stronger versions MX634 or MX632 may be advisable.

For scale 0, the stronger MX632 is recommended (except when there is a lack of space in a very small locomotives), even though at 1.2 A, the MX634, or at 1.0 A the MX630 seems nominally sufficient.

ZIMO decoders can withstand a heavy overload for a limited time (50 to 100%, up the "peak power" shown below). How long the decoder lasts depends in practice on the heating and hence of all the above-mentioned influencing factors. In average cases, the "peak current" can be withstood for 20 to 30 sec (provided the decoder has not already been worked close to the maximum), currents in the intermediate range between maximum continuous and peak power are of course permitted for longer, usually a few minutes. The decoder can overcome the usual gradients on a model railway, despite some over-current situations, so long as the decoder is subsequently cooled again ...     

While the "maximum continuous current" is controlled by the long-term heat load on the decoder,  the "peak current" is the threshold where electrical current is itself  the load limit (even with a hypothetical perfect cooling). That does not mean that a modest excess of the peak current would cause an immediate shutdown, but there are also a few seconds or milliseconds of tolerance, the closer the current is to full short-circuit current, the faster the cut-off. The fastest possible shutdown (at the next current pulse of 20 kHz) is activated on reaching the short-circuit current value which, depending on the decoder type, is between 4 A and 10 A.

 The above behaviour applies to modern ZIMO decoders, as they use a very sophisticated process so as not to produce unnecessary shutdowns, and still be safe. Simple and cheap decoders (from other manufacturers) often have a simple cut-off threshold. 

In the event of engine shutdown for exceeding the peak current or short circuit, an automatic re-starting occurs after about 3 sec, but there is no display (no blinking LEDs as when switching off due to overheating), but, as part of RailCom, appropriate alarm messages are sent to the controller.

ZIMO decoders have different types of outputs, the presence, number and capacity of the various outputs varies across the decoder families :

 - "Normal" (often called "amplified") function outputs, as exists in decoders for all manufacturers, and are (technically) "open-collector" or "open drain" outputs to which head lamps, other lights, smoke generators, coupling coils and other devices may be connected, with the second terminal of each device
- connected to the "common positive pole" of the decoder (blue wire), or 
- connected to the "low voltage" (purple wire), if the decoder has such a wire (MX632V, MX632W);
- It is also possible to connect the second terminal of a device with the left or the right rail,
 (In some vehicles this is through the conductive chassis, often where lights are used this is the case), with
  the device (in this case) has current flowing through it only half the time (for symmetrical DCC signal),
  So for example light with reduced brightness light (but in the perception but more than HELB so bright ..).

- "Logic Level" (often called the "unamplified") outputs, see below!.

- "LED Outputs", see below!

- Outputs for Servo Control, see below!

For the sake of saving space, the output current of the function output is recorded in total (all outputs together or in groups). The single-function output is strong enough in design that one can cope alone with the the total current (if required).

The shutdown in the event of a current overload is not immediate, but depending on the magnitude of the excess within a few tenths of seconds or milliseconds. This allows for example cold start of the lamps (if there is a problem,, the effect of "soft start" can be assigned).

"Logic Level" outputs, also called "unamplified" outputs or "logic level" referred to, which at the terminal a voltage level set (0V for "off", 5V for "on"), the max available has an internal protection resistor 10 K  (i.e. 0.5 mA output current), which by external gain can be made ​​available, which can be installed by yourslef, but there is also the M4000Z for this, see the detailed instructions for the decoder.

ATTENTION: "logic level" outputs are active in the default configuration of the decoder NOT because they use the same ports as the SUSI interface (clock and data) as well as the servo-control lines. The decision on the use of these common terminals is done with

CV # 124:     Bit 7 = 0  ->  SUSI      Bit 7 = 1  -> "Logikpegel"

and the CV's # 181, 182 (if these are set: the common terminals are used for servo controlt).  

"Logic level outputs" of the "C" and "D" types:  In all decoders with 21-pin "MTC" interface (either a "D" - type or a "C" - type, e.g. MX634D. MX634C or MX644D), these two variants (C and D) differ in each case by the execution of the function outputs FA3 and FA4:

"D" - type: FA3, FA4 are "normal" amplified output, "C" - Outputs: FA3, FA4 are "logic level" outputs

LED Outputs are special forms of logic level outputs, i.e. stronger (up to 10 mA) and with an LED series resistor (330 ohms) provided so that the direct connection of an LED is possible, which is switched to the opposite pole (ground) of the decoder (not to the positive pole as usual!) ; "LED outputs" are always usable as "logic level" outputs (i.e. with external amplification).

"LED outputs" have only available on those decoders that have efficient power (i.e. a switching regulator) for the microcontroller (3.3V or 5V) - causing little heat, and these are generally sound decoders such as MX640 and MX642.

Outputs for servo control, can use commercially available servos (Graupner, Robbe, etc.), for which various operating modes and end positions, orbital periods, etc. can be determined in the CV 161-182 range. For decoders with low voltage output 5 V (MX632W) the operating voltage for the servos is provided by the decoder; at MX644, this is entirely the case (only for small servos), otherwise, the 5 V voltage is generated externally, see instructions in operating manual.

The servo outputs using connections for the SUSI lines (clock and data), and are

CV's # 181, 182 are activated, but then SUSI is no longer available

Note: with the MX644 and MX646 family of decoders. the servo-control line is to 3.3 V level (standard requirement is 5 V, as provided in other decoder types), and the function is not sure to work with all the Servo brands.

The "SUSI" interface itself is a relic of the days when it was difficult to accommodate the sound generation in the decoder itself, and therefore separate own sound modules were introduced, with SUSI data lines (clock and data) which were controlled by the decoder. Even more function outputs could be provided in this way. These add-on modules, are still on the market many years later, although this solution is not technically up to date and there are functional limitations associated with it.

Although the original "SUSI" support is virtually obsolete now, all the ZIMO decoder have functioning "SUSI" connections (which do not cause a significant cost), because in the future these connections certainly could be used again, though perhaps with a modern, probably faster transmission protocol to allow communication between the locomotive (locomotive decoder) and attached cars (or function decoder) via conductive coupling. Such a "train bus" is actually provided in the standard decoder plugs (MTC - and 21-pin PluX) . Another use of "SUSI" interface would be linked to environmental sensors (tilt, lateral acceleration, GPS, ...) modules and train radio beacons or readers in the vehicle.

Energy storage in the form of an attached decoder can provide for bridging of power interruptions and to compensate for fluctuations in demand, has great benefits in several ways,
even very small capacitors of 100 µF show a positive effect (see list below), larger - up to several 1000 µF - even more, larger values ​​than about 5000 µF are NOT recommended
(due to possible overloading of the charging circuit).

The direct connection of Goldcap capacitors is NOT supported, and can cause problems!

ZIMO has recommended the use of energy storage capacitors for a long time (for all decoders), however, until 2009, some additional components (in the set available as SPEIKOMP
or SPEIGOMP) were needed around the capacitor to avoid disruptive effects on programming, on the loco number recognition and with respect to the "in-rush current" (high charging
current during power-on, can overload the command station).

From 2010 ZIMO decoders, initially MX632, MX631, and shortly thereafter sound decoder MX642, have made it possible to connect capacitors without additional components on the
circuit, which is much more convenient and at no additional cost.

The benefits of energy storage through an external capacitor are:

- Avoid stalling and flickering light on dirty tracks or turnout frogs,
    especially together with the software feature of the "avoidance of stopping on the de-energized points" (existing in all ZIMO decoders), generally from capacitor values of 1000 µF ,

- Reduce heat, which is caused by reactive consumption in the decoder, especially for low-impedance motors, effective starting at a capacity of about 220 µF.

- Using the technology RailCom: avoidance of the energy loss due to the "RailCom gap", reducing
  the engine noise caused by RailCom, improved signal quality RailCom (= readability), already effective at a capacitor of about 220 µF.

- Even with the ZIMO "signal dependant speed control (HLU)"  the energy loss due to the "HLU-gap" will be compensated.

In the packaging of the respective decodera small capacitor (e.g. 220 µF) is included as entry into the energy storage technology, more and larger capacitors can be obtained from
electronics stores or ZIMO.

Some decoders types (MX632) contain a built-in low voltage source, fixed at 1.5 V (V-type) or 5 V (W-type) or adjustable (MX635, MX636), which is used for the function outputs, and can be used as an alternative positive,  ("blue line") . The low-voltage source is based on an efficient switching regulators, producing less heat loss, such a low voltage is used:

- to operate low-voltage lights (usually 1.2 or 1.5 V) for head lights and other lighting applications,

- For the operation of LEDs, in this case the 5 Voutput is used, and the LEDs connected via a resistor of 330 ohms (for example)
- thus, less energy is "burned" than if the lights are operated on the full voltage, connected via a 1K ohm resistance (for example).

- For the supply of commercially available servos (5V), with the control via the servo output lines of the ZIMO decoder.

The use of the low-voltage supply has the added benefit that it is a stabilized voltage which remains constant regardless of any fluctuations in the rail voltage supply, and can be used by an energy storage capacitor free of interruptions at the rail.

Inputs are mainly important for sound decoders as they are used for connecting axle detectors (for axle based triggering of the steam chuffs) or position-dependent activation (by reed contacts, ..) of sound features, for example, the warning whistle before a tunnel or level crossing.

Note: The logic-level outputs of the ZIMO decoder (see above) could also be used as external inputs, if this is needed and supported by an appropriate version of the software, and these external inputs can function as switching inputs (to control position-dependent lighting effects or loco-controlled shuttles). This also applies to non-sound decoders.

Such outputs are naturally only available in sound decoders. Everywhere can be used 8 ohm speakers, of which there is a very large selection available from electronic component stores (e.g. Maplins, Conrad etc.), and some types can be ordered by dealers direct from ZIMO. For MX644 and MX645 (audio power up to 3 W) 4 ohms speakers are also suitable, or 2 (or 3) 8 ohm speakers can be conneted.

Recommendation: Particularly efficient (i.e. high volume with a small footprint) are the two miniature rectangular speakers with integrated sound chamber (part numbers LS10X15 and LS8X12) from ZIMO delivery program. These two types are normally built into mobile phones, and are rarely available on the market (especially with the sound chamber).

During selection of the speakers, of course, the bigger the better, also very important for a professional installation, are the resonant enclosure or an airtight locomotive housing with a sounding board and openings in the housing, etc.

Note: Often in vehicles there are built-in speakers of 100 ohms or 32 ohms, because it was favored in the past by some sound decoder manufacturers (as this results in a cheaper amplifier circuit on the decoder). These speakers are also usable by ZIMO decoders, but this mean a corresponding loss of potential sound volume.

ZIMO sound decoders use digital audio amplifiers, which are supplied in each case by a regulated 5 V. This solution produces a sound uninfluenced by fluctuations of the power supply, and is also fully available on analog DC systems of over 5V.

A sound-memory of 32 Mb corresponds to a playing time of 180 sec in the higher quality (22 kHz sample rate) and 360 sec in the lower quality (11 kHz). Sound projects supplied by ZIMO mainly use high quality sound samples of 22 kHz .

Note: Decoders with wires are shipped with transparent shrink tubing (insulation protection), but these photos show them without heat shrink tubing.

       MX615 (8.2 x 5.7 x 2 mm)                              MX621 (12 x 8,5 x 2 mm)                 MX622  (14 x 9 x 2,5 mm)                  MX623  (20 x 8.5 x 3.5 mm)                      MX630 (20 x 11 x 3.5 mm)                    MX634 (20.5 x 15.5 x 4 mm)  

          MX632 (28 x 15.5 x 4 mm)                MX645 (30 x 15 x 4 mm) SOUND                 MX648 (20 x 11 x 4 mm) SOUND           MX649 (23 x 9 x 4 mm) SOUND    

                                                                                                               

                                                               MX618N18  (15 x 9.5 x 2.8 mm)                                                   MX658N18  (25 x 10.5 x 4 mm)  SOUND

  MX615N (8.2 x 5.7 x 2 mm)                    MX621N (12 x 8.5 x 2 mm)           MX622N (15 x 9 x 2.5 mm)           MX649N (23 x 9 x 4 mm) SOUND

           
               MX634D   (20.5 x 15.5 x 4 mm)        MX632D  (28 x 15.5 x 4 mm)        MX644D  (30 x 15 x 4 mm) SOUND

 Information about the 21-pin "MTC" plug on "D Decoders" und "C Decoders", and their usage

Depending on the vehicle, the MX634D (or MX632D or MX644D) are plugged in from the top or bottom in the respective locomotive-board;  (the  tamper-proof pin 11 ensures the correct orientation) 

This applies to all "D-decoder" and "C-decoder" types; here (on the right) is shown the example of an MX64, the forerunner of MX631D. 

WARNING: in many cases  a "C-type" should be used instead of a "D-type", because Logic level outputs for FA3, FA4 are needed, especially locos from: Märklin, Trix, LS models, ..
.

                                                                                 

                                        MX620P12 (25 x 11 x 2 excluding plug)                           MX623P12 (20 x 8.5 x 3.5 mm excluding plug)     

               MX630P (20 x 11 x 3.5 mm excluding plug)      MX648P16 (20 x 11 x 4 mm excluding plug)SOUND     MX645P16   (30 x 15 x 4 mm excluding plug) SOUND

                  
                                    MX633P22  (22 x 15 x 3.5 mm excluding plug)           MX645P22  (30 x 15 x 4 mm excluding plug) SOUND