The Control Unit is the heart of the Digital System. Only one is required for a layout and other control devices plug into it. The Control Unit receives its power from a transformer by means of the yellow (labeled "L") wire and the brown (labeled "O") wire. Any transformer will work as long as it has a 16 volt fixed AC output, but one that supplies 42 watts, as the 6001 Märklin transformer does, would be best. Transformers that give more than 50 watts would not be any more productive since the Control Unit will not output more than 50 watts. The control panels will take about 8 watts to run and each of the engines take no more than 10 watts, so larger layouts will require an additional Booster to power them.

The Control Unit connects to the track with another brown wire and a red wire (labeled "B"). Extreme care needs to be taken so the wires are attached correctly and that they are connected when the power is off. Always unplug the transformer or turn its power off if you have it connected to an outlet box with an on/off switch. Computer electronics are very sensitive and switching wire with the power on can cause damage. The wire connectors at the back of the Control Unit are colored to match the wire that connect them to either the transformer or the track. The small red LED on the upper right of the black plastic facing of the Control Unit will light up when the unit is attached correctly to the transformer and power is turned on.

On AC systems the feeder tracks usually come supplied with a brown and red wire which will attach to the Control Unit, the brown wire connects to the outside rails and the red is connected to the center rail. With DC systems it doesn't matter which rail is connected to the wires. Connectors at the rear of the unit are designed to accept bare wires, not the typical Märklin plugs such as those found on the end of the feeder track wires. You will probably need to extend the length of the feeder wires anyway, so connect it to an extension wire with a Märklin socket and leave the other end bare for attachment to the Control Unit. If you have a soldering iron it is a good idea to solder the bare wire to make it easier to insert it into the connectors on the Control Unit. Also, be careful to insure that the bare wire and not the plastic insulation is in contact with the connector. Inserting the wire too far into the connector will cause it to make contract with the insulation instead of the wire and no power will be delivered through the contact.

Control 80f units and Interface units attach to the right side of the Control Unit either directly or by means of one of the extension cables available from Märklin. The 6038 cable is 72" long which allows you to control the train from a distance of 6 feet from the Control Unit, and the 6039 cable is 25" long. The shorter cable separates the control devices enough so train operators can stand side by side at the control panels. Once a Control 80 unit is plugged into the Control Unit, other controllers or an Interface can be plugged into their right side also, either directly or with a cable.

The Control Unit allows for up to 10 Control 80 units to be connected to it. These 10 controllers can control any of the 80 locomotives on the track. The Control Unit has a memory that keeps track of which locomotive is currently being addressed by any of the Control 80 units. If another person addresses that same locomotive on another Control 80 the Control Unit will flash the second operator's LED screen to notify him that the engine addressed is currently under the control of another operator.

Keyboards attach to the left side of the Control Unit. They also can make use of the cables to separate multiple operators into comfortable distances. Of course, if only one operators is controlling the switches on the keyboard, then you would want the components to be close together.

In the event of an overload or short circuit, locomotives will stop and the additional functions are switched off and the LED on the Control Unit will go dark. If the disturbance lasts less than two minutes, just press the green "go" button on the Control 80 to resume normal operation. In the event of longer disturbances, all commands must be reprogrammed.

It is possible to design a layout so more than one Control Unit is present. That type of arrangement would require blocking the track sections so the two units wouldn't conflict with each other. This type of operation would resemble the conventional layouts with block of track being operated by different transformers or cab controllers. The primary difference would be that you must remember that when moving from one block to another, the same engine address must be entered in the different control 80 units, and a bridge for the center rail pickup shoe should be incorporated into the track.

The reason why someone may want to use more than one Control Unit lies in the fact that only ten Control 80 units can be connected to a single Control Unit. Club layouts that provide the potential for dozens of members to operate trains simultaneously would want to have the option to have more than ten users at a time. Other situations that would require more than one Control Unit are where layouts have more than 256 switches. That would require more Keyboards and addresses than can be attached to one Control Unit.

The Central Control-i Unit has the capability of controlling four locomotives with the addresses 10, 20, 30 and 40 through the green buttons labeled one through four. It will also control one accessory decoder unit such as the k83 or k84 which controls four switches or signals. These accessories are controlled through four buttons similar the the ones found on the Keyboard. Each has a red and green setting and will control momentary solenoids such as the ones found in signals and track turnouts through the k83 decoders, or will control constant current accessories such as motors through the k84 decoders.

Further control is achieved by adding keyboards and a Control 80f to the Central Control-i Unit. However, with the built-in computer interface, full control can also be achieved through a computer.

One noticeable change with the new communications is that you will get greater reliability with the 4 auxiliary functions and the one loco function if the loco is equipped with them, and you will get true direction notation on the panel of the 6021. After the readout of the loco address there are two arrowheads, one could be lit which points up, or the other points down. When the arrow is up, the locomotive operates forward and when down it operates in reverse (note: if you attach a 6035 or 6036 Control 80f to the right of the 6021 you will not see the direction arrows next to the address). The four auxiliary function commands are now being sent with the 1 Gauge loco commands. In the past, those function commands were sent separate at the same speed and with the same format as the other accessory commands (i.e. turnouts and signals).

Other differences which might not be as noticeable include greater reliability of the locomotives response to commands. There will be no more random reversing when the locomotive is traveling at speed seven and the function is on. Also, the timing between the commands is shorter giving a quicker response time from the locomotive. Switch 4 is connected to the power output of the 6021 and when it is on (up) it is designed to operate 2-rail type DC powered HO layouts which might only need 12 volts of current. Keep this switch down for 1 Gauge and you will get the maximum current available.

Maxi locomotives can be controlled on Digital 1 Gauge layouts without any adverse affect. This is also true of other large scale locomotives with Maxi or 6095 decoders installed in them. None of the new 1 Gauge decoders will work with the older 6030 Control Control-1 or the HO versions 6027 or 6029. Those units were developed for 2-rail only and used a frequency modulated signal. Märklin's Digital program currently uses the same data stream signal (Motorola format) which has been successfully used since the Digital program began in 1984. This Digital system is capable of controlling 2-rail and 3-rail layouts with both AC and DC locomotives. With the 1 Gauge system you have a 2-rail track layout which could have both AC powered 1 Gauge locos and DC powered Maxi locos running at the same time.

The 6095 decoder has a slider switch which allows for three different modes of operation:

Switch setting

left: - Digital (Motorola format)
center: - Alternating current (~)
right: - Direct current (=)

The 5739 self-propelled crane car (on the alternating current version - not the 5740 direct current version) comes from the factory with an electronic circuit which can be controlled with Märklin Digital after it has been coded with solder bridges. This coding procedure should be carried out by a Märklin dealer. It should also be pointed out that this model can no longer be operated conventionally with alternating current after it has been coded.

The 6095 decoder has acceleration and deceleration delay settings similar to the 6090 decoder used in HO scale locomotives. Two rotary potentiometers on the electronic circuit plate change the acceleration and deceleration delay or the locomotive's maximum speed. Note: The braking delay is active only with digital operation, the other settings will be active in any operating mode (i.e. AC, DC or Digital).

Potentiometer #1 sets the acceleration and deceleration delay. Clockwise increases the maximum delay, counterclockwise increases the minimum delay. Pot #2 changes the maximum speed setting. Clockwise gives a lower maximum speed and counterclockwise gives a higher maximum speed. The load-dependent speed control works automatically (constant speeds up and down inclines). For technical reasons this control is not so noticeable in the AC or DC operating modes as it is in the Digital mode.

To operate the four auxiliary functions (f1-f4) the locomotive address must agree with the function decoder address. Both the red LEDs over the "L" and "F" light up at the same time when the address is called up.

Mixed Digital and conventional layouts are no longer permitted with the 6021 Control Unit and 6095 decoders. Running a locomotive from a digital section of track to a conventional section may damage the electronic components.

When attaching the 5625 turnout mechanism and the 5613 signal to the k83 decoder, the following connections need to be observed:

5625 turnout or 5613 signal k83 decoder

connection 1 - - - - - - - - - - - -> green socket
connection 2 - - - - - - - - - - - -> red socket
connection L - - - - - - - - - - - -> yellow socket

single motor 1 locomotive <15 VA
double motor 1 locomotive <25 VA
smoke generator <5 VA
turnout when activated <10 VA
light bulb approx. 1.5 VA

The new 6021 has the plug inserted and soldered correctly on the printed circuit board, but that requires a different plug and cable connection at the rear of the Control Unit. If you are using the 6021 with a booster the wire leaving the plug at the 6021 should be directed up; this is true with the 6017 booster as well. If you connect to an older 6015 booster, the wire leaves the plug at the 6021 going up and enters the 6015 from under the plug.