Märklin Digital was among the earlier digital model railway control systems. It was a comprehensive system including locomotive decoders (based on a Motorola chip), central control (Märklin 6020/6021), a computer interface (Märklin 6050), turnout decoders (Märklin 6083), digital relays (Märklin 6084) and feedback modules (Märklin s88/6088). The initial system was presented at the 1979 Nürnberg International Toy Fair, released in Europe in 1985 and the USA in 1986 under the name Digital H0.
Operation Conventional analog control of model railways works by varying the track power and any locomotive on the track will respond by running at a speed roughly proportional to the power. For multiple trains, sidings must have a switch to isolate trains standing there and leave the track dead. For multiple controllers, the layout must be divided into sections isolated from each other and each with its own controller and current supply. All accessories such as signals and turnouts require individual switches and cables, making wiring very complex.
With analog systems, fine control of locomotives requires knowledge of the individual characteristics; gradients and curves require constant adjustment and low speed running is both difficult and liable to stalling. Any train lighting will vary in intensity with the power and be off when the locomotive is stopped.
Digital control supplies constant power to the track with the power being switched many times a second to provide the "bits" of data (0 and 1) necessary for control (such digital power is neither DC nor AC). Every locomotive must be fitted with a decoder circuit which will interpret instructions and individually control the motor. Each decoder has its own address, instructions sent from the controller have a corresponding address so that while every active decoder will receive the instructions only the addressed decoder will respond. Once a locomotive is running it will continue and so even with one controller several trains can be running.
Many locomotives may be on the track and individually controlled. Train lighting will always be at full intensity, even when the locomotive is stopped. Signals and turnouts may also be provided with decoders and controlled digitally. The track consists of 2 electrically grounded rails, and a row of center studs over which the engine's pickup "shoe" glides acquiring the digital-pulsed 16V signal and power. This symmetrical track design solved the problem of loop-back topology (a problem encountered in polarized 2-rail). Conceptually, the entire layout may be controlled from just two wires to the track, but in practice multiple feeds will be required and power to the track is usually separated from power to accessories.
The final step to ideal running was the development of motor regulation or speed control (often misleadingly called "load control"). Locomotive motors are controlled using pulse-width modulation which gives much better regulation than conventional analogue control. Additionally, utilizing the full track power available, decoders can use motor feedback and constant adjustment to maintain steady speed regardless of train load or track gradient. Combined with braking and acceleration delay (artificial inertia) these decoders give smooth and exact speeds with reliable slow speed control.
A number of different digital systems were developed, but Märklin Digital and DCC (Digital Command Control) are the two main systems on the market. The systems are electrically compatible and some controllers can simultaneously control both types of decoder. Märklin offered versions of their original digital system for 2-rail users.
Märklin Digital Märklin first presented the new digital control system at the Nürnberg Toy Fair in 1979. The Motorola based system was officially introduced in 1985, developed by a relatively unknown electronics contractor with most components built by Märklin. In subsequent years, another contractor, Bernd Lenz, would also work on the system producing locomotive decoders and, later, Märklin's first DC command control offering. This first DC offering was later developed into what is now known as Digital Command Control (DCC).
The new Märklin Digital system offered simultaneous control of up to 80 locomotives and 256 accessories. 14 locomotive speed steps (stop 0 and 1 - 14) were provided and an accessory "Function" that was used for locomotive front and rear headlights or TELEX remote uncoupling.
Electronics of the time were relatively expensive and the system used ternary logic to reduce the number of components and cost of devices. Early decoders cost as much as many model locomotives and the expense of upgrading an existing layout was considerable.
Controllers The original 6020 Central Unit provided track power & generated locomotive commands but required a separate 6035 locomotive Control 80 with speed controller, keypad for decoder address, Function / Off buttons, and Start / Stop buttons to switch track power. The red Stop button was provided as an emergency stop to immediately halt all trains. A two digit display showed the selected locomotive address (01 - 80). Solenoid devices, such as turnouts, were controlled by the 6040 Keyboard. Up to ten controllers could be added to the right hand side of the Central Unit, and up to 16 keyboards could be added to the left hand side, with each keyboard controlling 16 accessories (signals, turnouts, lights, etc.) for a total of 256. For large layouts 6016 Boosters and their own power supplies would provide additional power to layout sections with all Boosters linked to the Central Unit by a ribbon cable.
A later accessory was the 6043 Memory, which was used for switching predefined routes each with multiple turnouts & signals. The 6043 could save up to 24 different routes, which each route containing up to 20 individual device commands. The 20th command in one route memory could be used to link to another route button, so there could be a large number of individual commands enacted by pressing one button. In addition, the 6088 s88 Feedback Module could be used in conjunction with the 6043. The s88 would receive input signals from external buttons or magnetic reed switches and then start a command string in the 6043 Memory. So, an approaching train could set up its own route, as an example. Another accessory was the 6050 computer Interface which let the system be computer controlled, allowing for fully automated train control.
Decoders The first c80 (6080) decoders did not have motor regulation (speed control) and the 1991 introduction of c90 (6090) decoders with regulation and a 5-pole DC motor brought the system to maturity. Decoders had miniature switches (DIP switches) to set the address and c90 decoders had two potentiometers to adjust braking / acceleration delay ("inertia") and maximum speed, requiring the use of tools to open the model and make any changes to settings.
Accessory decoders Signals, turnouts, uncouplers, lights, and other static accessories may also be fitted with decoders which have their own address range for up to 256 switched devices. Depending on the decoder, either continuous power (lighting) or momentary (signal, uncoupler, turnout) is provided. K83 decoders are for solenoid (momentary) accessories and K84 for lighting (continuous) accessories, each one controlling up to 4 devices.
Automatic braking Automatic braking allows a locomotive to coast relatively gently up to a stop signal at danger. When fed with negative DC the decoder will slow the locomotive smoothly. Track must be sectioned at least once, the stopping area before the signal, and usually also a transition section to prevent short circuits. An electronic control module is switched when the signal changes to danger and changes the track voltage in the stopping area.
Märklin Digital (new) In 1993 an enhancement to the original system introduced improvements for locomotive control:
Additional four switched functions F1 - F4 Absolute direction control with direction sent as part of speed commands
The changes were entirely compatible with earlier locomotive decoders so any controller was able to control any locomotive decoder type (a few special function decoders developed earlier were incompatible with the revised protocol, 6021 control units could be set to send old protocol only).
Absolute direction control is important for computer controlled layouts so that, after power off, locomotives will restart in the previously controlled direction. Older c90 decoder equipped locomotives will always restart forwards after power off, regardless of the previously controlled direction.
Controllers The new 6021 combined control unit & locomotive control with additional function buttons. Miniature switches set the operating mode (old or new protocol) and reduced track voltage for shunting areas.
The new Control 80f allowed additional locomotive controllers to be plugged into the right hand side of a 6021, other modules as before.
Decoders 1997 c91 (60901) decoders provided additional function outputs F1 - F4, 27 speed steps (stop 0 and 1 - 27), and improved motor regulation. Although the new decoders had 27 speed steps, existing controllers could only send 14 and so the decoders would step up odd steps and down even steps making all 27 steps accessible.
The extra functions allowed for other features such as additional lighting and sound. While the small size of speaker that can be fitted into H0 locomotives limits reproduction, built in sound has become a feature of many models. Adjustments to the new decoders required tools, as before. "Function" was most commonly used for locomotive headlights, F1 & F2 were usually used for other power functions such as smoke units or additional lighting. F3, when available, was commonly used for sound, and F4 usually used to disable artificial inertia for precise control, especially when shunting.
These decoders are now designated "fx" to distinguish them from earlier decoders lacking additional switched functions.
Function decoders Function decoders without motor control can also be fitted to carriages providing the 5 switched functions to control train lighting and other additional features. They may also be fitted to locomotives lacking the additional switched functions (i.e. c90 equipped locomotives). Function decoders require their own address from the 80 addresses available for locomotives (the address can be shared with another decoder lacking additional functions). Märklin had offered some special models with additional functions for the original digital system, but separate function decoders only became available with the enhanced system.
DELTA A simplified system intended to appeal to beginners and those put off by the then substantial cost of full digital systems, DELTA offered control of up to four locomotives simultaneously. DELTA decoders did not have motor regulation and initially lacked any way of easily changing the address. DELTA has now been discontinued, simplified digital controllers & decoders are offered instead (Mobile Station & 36xxx series locomotives).
Early DELTA controllers lacked the Function / Off buttons and c80 Digital models running on DELTA had Function permanently on which affected any such models equipped with TELEX remote couplers. c90 models running on DELTA had Function permanently off.
Märklin Digital (mfx) In 2004 the completely new Märklin Systems digital control was unveiled. A new two way protocol can control up to 65,000 digital devices, each locomotive can have up to 128 speed steps and 16 functions. Developed by ESU with all components initially made by them for Märklin, later the name "Märklin Systems" was dropped and once again the system is known as "Märklin Digital".