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An overview of DCC. Following the overview is a simple tutorial for getting a basic DCC starter set up and running.

[edit] Define DCC - In a nutshell

DCC is an acronym for Digital Command Control. It's a method of taking information from a throttle (think: train controller), having it processed by a command station, and sending it out as a digital packet to the entire track layout.

Each locomotive on the track is equipped with a decoder. Each decoder is programmed with a unique address. A decoder looks at all the digital packets that zip past on the track, looking for packets with its own address.

Once a locomotive sees a command addressed to it, it performs whatever function it's told to do - such as stop, speed up, slow down, turn lights/on and off, or turn on/off various engine sound effects.

DCC is a model railroading industry standard and is regulated by the NMRA with the cooperation of the manufacturers. The standard is defined at the rails. This means that locomotives equipped with decoders from different DCC Manufacturers may be used with any brand DCC setup. Though low end basic command stations may not support all advanced decoder functions, they will still be able to control direction, speed, and basic lighting functions.

And now..in layman's terminology.

[edit] The way it was

Before the digital world, we lived in the analog world. The speed of a model train was controlled by how much DC voltage was applied to the rails. The higher the voltage, the faster the locomotive moved. To change the direction of the train, you simply flicked a switch which changed the polarity on the rails.

The problem was that you could only run one train at a time. If you wanted to run the train around on a loop to go back from where you came from, you needed some fancy switches and wiring. This leads us to...

[edit] ...Block Control

In order to control two trains, with different directions and speeds, you had to rely on "block control". This involved lots of wiring and double-pole double-throw (dpdt) switches, which divided a layout into sections or blocks. By dividing the layout into separate blocks, you could control whatever train was in that block. If you wanted to take your train from one block to another, you had to check and make sure that the dpdt switch was thrown in the right direction. The throttle didn't control the train, it controlled the track. When the train passed from one block to another, you had to change the track you controlled in order to maintain control of the train... and if the two trains somehow ended up in the same block, there was no way to do anything about it.

However, if you wanted to run more than two trains, you had to install a whole bunch of special rotary switches - a complex and expensive proposition. This required an array of power supplies and throttles (one for each train), switches, and wires. The more complex and detailed your operating scheme, the more complex the wiring. All helper districts and yards had to be carefully preplanned. Adding a single operator and train to your schedule might require rewiring most of the layout! There had to be a better way!

Now, fast forward to today and the world of DCC.

[edit] DCC Control

[edit] Clear Your Mind

Forget everything you know about running your layout using the good-old-fashioned DC power pack. Most magazines, how-to books, websites, and other media compare DCC to DC. Forget it! Drop it! Erase your mind! Running your layout using a good-old-fashioned DC power pack no longer exists!

[edit] The Networked Computer

Now that you've erased you-know-what from your mind, let's take a look at how a bunch of computers, printers, scanners, servers, modems, and other devices are hooked together to form a computer network. If you work or study in an environment where computers, printers and other devices are connected together in a network, you're well on your way to understanding Digital Command Control.

[edit] The Basic Computer

We have a basic computer in front of us. We type on the keyboard to enter instructions. We move the mouse and right-click, left-click or middle-click to enter more instructions. We get a visual display of what we are doing on our monitor. In regards to DCC, we'll call this computer a throttle.

[edit] The Server Computer

Not all computers have the same capabilities. Your computer might have a modem, a scanner, a joystick, a printer. In an office environment, you might have a server that has more memory, larger hard drive, and more powerful software. A server computer in the DCC world comes in the form of a command station.

[edit] "Hooking Computers Together"

Let's connect your computer and my computer and our friend's computer together in a "local area network" or LAN. This way, we can share resources. Instead of a whole bunch of small inkjet printers, everyone can use a faster laser printer hooked into our network. We can even add a colour printer to the network, a scanner, a fax machine, a modem, or many other different types of devices to our network. *This is the power of a networked computer system.*

[edit] Recap

So, let's recap all of this. We have a bunch of computers (with keyboards, mouses, monitors attached), printers, scanners, CD-ROM burners, modems, servers, etc. Some computers are more powerful than others. Some computers have extra devices attached. All of these computers, printers, devices, etc are connected together by a network. All of these computers, printers, devices, etc communicate with each other through this network.

We've probably over-simplified the situation - but you get the picture? If you don't here's a picture for you.

[edit] So What's DCC Got To Do With Computers?

Most of us are familiar with computers, so let's apply some of this computer terminology to model railroading.

I have a computer in my hand (we call it a throttle). On this hand-held computer (the throttle), there's a keyboard, mouse, and monitor (knobs, buttons and display). This hand-held throttle is plugged into a computer network (Digitrax calls it the Loconet; Lenz calls it XpressNet).

If I want to send a message (stop, go, increase speed, reverse direction, turn the lights off, ring the bell, blow the horn) from my computer via the network (the LocoNet) to your computer, I turn the knob or push a button on my computer (the throttle). This sends my message through the network (the Loconet) to a more powerful computer (a command station/booster - more on this later). This more powerful computer (command station/booster) amplifies and transfers my message along a different part of the network.

Because my message is addressed to your computer, only your computer will pick up my message sent from my computer. When your computer picks up my message, your computer will carry out the instructions that I sent to your computer. What does your computer look like in this model railroad scenario? Why it's your locomotive that you've let me use!

That's all DCC is - a networked computer system used to run trains! Some of these computers are called throttles, some are called Command Stations/Boosters, and others are called locomotives. We can add other computers if we want - more throttles - more locomotives - whistles, horns, bells - switch machine controls - signal systems - etc. etc. - by simply plugging them in. Not all of these "computers" have the same capabilities. Some of them might even be personal computers running one of many computer applications.

The only difference between a computer network and a DCC network are the tracks and the power in the tracks. Because we need a bit of power to run the locos, the power in the track is typically a continuous 16 volts at 5 amps. The electricity is alternating current - but not the type you're familiar with. We won't go into the details at this point - perhaps later on.

[edit] DCC: An NMRA standard

Products with this logo conform to the NMRA standards. Products with this logo use the NMRA DCC Standards. The NMRA Conformance seal is given only to system components that completely conform to NMRA standards. With NMRA conformance, decoders from numerous sources will always function properly with any conforming digital command station.

The National Model Railroad Association (NMRA) is an organization developed with the intent of the betterment of the model railroad hobby. They are making every attempt to standardize the industry by publishing DCC standards for manufacturers and consumers. Their trademarked symbols notify consumers the product(s) they are using (or may wish to purchase) meet the compliance standards set by the NMRA.

Products that use the DCC Standards and Recommended Practices can display the NMRA's DCC logo. To get an NMRA conformance warrant products are tested by the NMRA. There is some controversy about the higher conformance warrant and its usefulness. Some manufacturers had products tested and awarded the conformance warrant early in the history of DCC, but have decided that it is no longer necessary, though they still abide by the standards and participate in DCC development. Lack of the Conformance Warrant "football" seal is not necessarily an indication of a poor quality or incompatible product.

Standardization has lowered costs to the consumer, lead to more creative products, fostered greater interchangeability of equipment, encouraged more manufacturers, and allowed larger numbers of modelers to enjoy digital command control systems.

The backwards compatibility features built into the standard allows those modelers not interested in DCC to continue to use existing 12 volt DC standards without affecting the operation of their equipment.

[edit] What's next

We're going to assume that you fully understand the information above. If not, re-read it again.

Now, lets start the official DCC Tutorial.