One of the nice things about DCC is that you not only have individual control of each loco irrespective of where it is on the layout, but you also have independent control of other electrical devices on each loco or train. How many things you can control depends on how many functions the decoder has and how it is wired.

With DCC, track voltage is constant all the time. This allows lighting functions that can be controlled regardless of whether the train is running or not. So, if you want the headlight on, you turn it on - at any time. If you want it off, you turn it off - at any time. Further, other lights can be controlled while providing special lighting effects such as Mars lights, Blinking Ditch Lights, and more. A loco could have front and rear light, Mars light, Blinking Ditch Lights, number board lights, truck lights, and running board lights -all independently controlled. On top of all that, smoke units, coupler control, passenger car doors, and literally anything electrical on the train can also be controlled. Literally anything you can model or modify to be controlled electrically can be controlled with DCC - not only on the train, but anywhere on the layout. All these things can be controlled from a hand-held throttle that's plugged in anywhere around the layout, from a Radio, from an Infrared control throttle, or from a computer.

Control of the loco's speed and direction is not considered to be a function. When a decoder is advertised to have four functions, that implies that you will be able to control the train's speed and direction, plus four more things - such as headlight, rear light, Rotary Beacon, etc.

Typically, a decoder has a function wire that controls the flow of electricity from a blue common power wire. This function wire is connected to the electrical device you want to control, along with the blue common. When you have that loco selected and operating on the layout, all you have to do to turn that electrical device on is to press the function button that controls the function wire your device is connected to. Pressing the function button again will turn it off.

Functions are numbered from 0 through 12 - for a total of 13 functions. Currently, decoders come with anywhere from 1 to 9 functions. I don't know of any decoder that doesn't at least have Function 0 for the headlight, with most having front and rear directional lighting. As far as I know, the only decoder that uses up to Function 8 is SoundTraxx sound decoders. In the near future, there will be decoders that will allow some or all of their functions to be remapped to the higher functions.

Function wires are colored so you can tell which to use for which function button. The NMRA has set some wire color standards to help make this easier. Power pickup from the track is red and black, motor control is orange and gray, and the common (power lead) for all functions is blue. Following is the list of functions the NMRA has set a color standard for:

Function 0 forward - White (for front light)
Function 0 reverse - Yellow (for rear light)
Function 1 - green (usually the bell when sound is used, but otherwise can be for anything)
Function 2 - violet (usually the horn/whistle when sound is used, but otherwise can be for anything)
Function 3 - brown (isn't actually an NMRA standard, but is used by Digitrax as their standard)

Function numbers greater than 2 are not designated by the NMRA, so refer to the manufacturer's decoder documentation for wire colors of these functions.

Most functions simply provide voltage on/voltage off control. But there are other ways a function can work. The rest of this page will be about that and some of the things that can be done with functions.

As noted above, Function 0 can have two wires - one for the front light and one for the rear. The way this normally works is, when Function 0 is turned on the front light will be on when the loco is going forward and the rear light will be on when the loco is going in reverse. This is called Directional Lighting. Many decoders provide a way to separate the control of the white and yellow wires into two different functions. This provides two non-directional, independently-controlled functions. With Digitrax decoders, for example, programming a "01" into CV 61 provides non-direction on/off control of the white wire with Function 0 and non-directional on/off control of the yellow wire with Function 4. Other manufacturers may do it in other ways, so you'll have to check their documentation.

Most function buttons work the same way - pressing them one time turns them on, and pressing again turns them off. This is called a toggle function button. This is useful for most lighting and other applications - press Function 0 once to turn the headlight on, press again to turn it off. Function 2 is different (at least with Digitrax's systems). Function 2 is designed to control the horn/whistle - press it to blow the horn/whistle, release to stop it. This is called a momentary function button. Having a momentary function button for the horn/whistle allows you to easily play the grade crossing or other railroad control/informational tunes. However, if you want to use Function 2 as a toggle, there are ways to "lock" it on when the button is released. Pressing it again "unlocks" it and turns it off when you release the button - just like a standard toggle function button.

[Some manufacturers provide what many call FX Lighting. This term was coined by Digitrax when they came out with their FX Lighting in 1995. Actually, Throttle Up! (SoundTraxx) had these features in stand-alone products called HyperLights, long before DCC came along. While the HyperLights products have been discontinued, they still provide HyperLights in their sound decoders today. Some manufacturers use the FX term for special lighting effects, while others use variations of it.

Most people only use Function Control for lighting. We've got one customer that lights up everything - to a point of sometimes needing more than one decoder to handle it all. For the most part this is fairly easy to do. If you want Blinking Ditch Lights, for example, simply purchase a ditch-light kit (or scratch build the brackets to mount regular Grain-of-Rice bulbs up front), connect them to two functions of a decoder that offers the Ditch Light FX feature, and program it to do ditch lights. It's the same for the Mars light, rotary beacon, FRED, etc.

Some people go all out in their modeling. We have customers who control their smoke units with Function Control. Another has built a mechanism to control the coupler on the back of his tender, and one has made operating doors in his passenger cars that open when the train pulls up to the station. The station master then reads off the list of towns the train is heading to before hollering "boooooaard!" - all controlled with DCC from their hand-held throttles.

First you have to have a decoder that has at least one function for each thing you want to control. All decoders carried by Loy's Toys includes at least front and rear lighting. We also have decoders with anywhere from four to eight functions - some sound decoders have 9 functions.

To control these functions, you must have a system and throttle capable of handing the number of functions you want to control. For example, a SoundTraxx sound decoder has eight functions plus front and rear lights. To access them all requires a system and throttle that can access functions 0 through 8 - nine functions total.

Digitrax, Lenz, and Train Control Systems have function-only decoders available. The functions of these decoders are remappable. At least Train Control Systems' will have the capability to remap anywhere from Function 0 to Function 12.

All of Digitrax's current systems can access any function that the throttle is capable of controlling. The DT200 and BT2 throttles can control functions 0 through 4, the UT1 and UT2 throttles can control functions 0 through 5, the DT100 and DT300 throttles can control 0 through 8, and the DT400 can control 0 through 12.

Don't assume that other manufacturers' systems have this much functional control. MRC Command 2000 is an example of a system that has very limited Function Control - having control of only functions 0 and 1.