With DCC, you don't worry about where the train is located on the layout, which throttle you're using, or toggle switches to connect them together. You simply pick up a throttle, select the address (loco number) you wish to run, and run it. This not only includes control of the train's speed and direction, but also lights and other electrical functions on the loco and/or train.

DCC provides two ranges of addresses. The first is 0 through 127. This is called the "Primary" address. Other terms used for the Primary address are"Base address", "Short address", and "2-digit address" (even though numbers from 100-127 are three-digit numbers). The second range of addresses is from 128 through 9983. This is called the "Extended" address. Other terms used for the Extended address are"Long address" and "4-digit address" (even though numbers from 128-999 are three digit numbers). Note that the NMRA has reserved addresses from 9984 through 9999 for other future uses.

Which range you use depends on your preference or need. More about that later.

All DCC Command Stations, Throttles, and Decoders support two-digit (Primary) addressing to one extent or another. Four-digit addressing is a non-intrusive option. Even if your equipment has four-digit addressing, you don't have to use it if two-digit addressing will suffice for your needs and desires.

Note that when discussing addressing, there are two aspects of it: Programming and Selecting. Programming is the act of telling the decoder what address to respond to. Selecting is the act of choosing an address in order to run a loco. Programming is generally done one time - when you first get the loco (decoder). Once programmed for a specific address it will remember that address (even when power is turned off) until you change it. Unless otherwise stated below, use of the term "addressing" implies the capability to program and select addresses.

When using two-digit addressing, the address is kept in the decoder's CV1. Programming this CV is very easy with any system. See Programming for more information and a discussion of what a CV is.

When using four-digit addressing, the address is kept in CVs 17 and 18. With Digitrax's current four-digit throttles, programming the four-digit address is almost identical to programming the 2-digit address - obviously it can't be identical because there are two additional digits to enter.

How you select the address is dependent on the throttle you have. With Digitrax throttles, there are three different methods:

1) Address selection by key-pad. Press the LOCO button, key in the address, then press the LOCO button again. Digitrax has this selection method with their DT400 throttles. Many non-Digitrax systems use a similar method.

2) Address selection by Digital Encoder knob(s). Press the SEL or LOCO button (depending on the throttle), dial in the desired address, then press the SET or LOCO button (again depending on the throttle). Digitrax's DT100, DT200, DT300, and DT400 throttles have this selection method. Yes, DT400 can select addresses by key-pad or Digital Encoder knobs.

3) Address selection by rotary dial. These are little dials with numbers from 0 through 9 on them. Set the dials to the address you want and press the ACQ button. This is the method used with Digitrax's UT1 and UT2 throttles. To have two-digit addressing requires two of these dials, which the UT1 and UT2 have. To have four-digit addressing with this method requires four of these dials. Digitrax doesn't currently make a four-digit throttle with this type of selection mode.

Four-digit address selection usually takes a little more effort than two-digit addresses. How much more effort is dependent on the system/throttle you have. With Digitrax's DT400 throttles it's the difference between keying in four digits instead of two or dialing two knobs instead of one.

So, do you need four-digit addressing? Maybe, maybe not. Some people want to use four-digit addressing whether they need it or not - simply because they want to use the entire road number on the side of their loco. But experience shows that using two-digit addressing is easier - to a certain point.

A typical scheme is to use either the first or last two digits of the road number. The only requirement here is consistency. If you use the first two digits on some and the last two digits on others, you'll have a hard time keeping track of which two you used on which locos.

This two-digit scheme works to a point. On the surface one might think this is feasible for up to 99 locos on the layout. While it is feasible, it's not easily doable - and the whole point for doing two-digit addressing in the first place is to keep thinks simple and easy. Experience shows that when you get to around 25 locos on the layout, you start having more and more duplicates of the two digits you chose to use. The only solutions when this starts to happen are either to renumber some of the locos or to start using four-digit addressing. I think it's easier to do four-digit addressing than to renumber locos ­ you may be different.

You can have both (two- and four-digit) addresses programmed into a decoder at the same time. Which address the decoder will use is dependent upon the setting in Configuration Data #1 (CV 29). For more information about that, refer to CV Bit Manipulation.

Having both addresses present at the same time can be useful if you have a home layout using a two-digit address, but also take your loco to a club where a different (usually a four-digit) address is required. All you have to do to switch between them is set CV29 for the one you want to use. Since CV 29 can be programmed on the programming track or with OPS-Mode Programming, you can do it almost anywhere any time.

Digitrax's DT100 (discontinued), DT100R (discontinued), DT300 (discontinued), DT300R (discontinued), DT400, and DT400R, are all capable of programming and selecting all two- and four-digit addresses when used with a Chief, Empire Builder, or Zephyr Command Station. They are limited to two-digit selection on Digitrax's Big Boy system (discontinued).

Digitrax's Big Boy throttle, DT200 (discontinued), is capable of programming and selecting two-digit addresses when used on a Big Boy system. On Digitrax's other systems, it can select two-digit addresses, but cannot do any programming. Note that on a Big Boy system, only the Master DT200 can do programming. Other throttles, even if they have programming capability on other systems, cannot do programming on a Big Boy.

Digitrax's UT2 throttle is capable of selecting any address up to 98 and can acquire any address dispatched from another throttle. It can program any addresses up to 99 on any of Digitrax's current systems.

Digitrax's UT1 Utility Throttle is capable selecting addresses up to 98 and can acquire any address dispatched from another throttle. The UT1 does not have programming capability.

All locomotive decoders carried by Loy's Toys have four-digit addressing, but come with the two-digit default address of "03".

Four-digit addressing is a non-intrusive optional feature. Decoders come set for two-digit addressing and you do not need to learn about four-digit addressing unless you want to use it.