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Command stations are the heart of the DCC system. They receive commands from a throttle network (such as Digitrax's Loconet), processes them, and decides if it needs to make a DCC standardized packet to send to the decoders on a DCC system. They don't do the actual work, they tell other things to do the work.

[edit] Function

The command station listens for commands from throttles and other devices, processes them, and sends the resulting signal to the booster. The booster combines power from the power supply and the signal from the command station. The resulting output is a digital signal applied to the track. On the track are the locomotives, with their decoders. Other stationary decoders, like switch motors and crossing gates, may also be connected to the track to receive commands.

The command station is typically the limiting factor of a DCC system. It is responsible for keeping track of which trains are controlled by what throttle. They are also responsible for a host of other items, such as additional functions sent by the throttle.

For example, if your command station supports only 2 digit addresses, your decoders only see 2 digit addresses on the track, even though the decoder is capable of four.

Command stations vary from manufacturer to manufacturer, offering different levels of capability. Differences include the number of slots for running trains, the range of functions supported, the upgrade or expansion possibilities, the total output amperes available to the track, and the number of throttles supported. Make sure you understand what you are getting, so you will not be disappointed or overwhelmed with capabilities. Keep in mind you do not have to use all the features of a command station to get a basic layout up and running. It's easier to not use functions and features than it is to add these later on - adding features usually requires a new command station!

Of course, prices vary based on the features of the command station. Be sure to do your research on various brands and models before making a selection. Some command stations will limit the features available, whereas others are only limited by the features of the throttle connected to it.

Note that in most cases Command Stations of various vendors are incompatible with each other.

[edit] Data rates

The command station is able to transmit between 150 and 200 packets per second to the decoders. You might be asking "Is that a lot?" Let's put this into human terms.

Let's say there are 10 decoder-equipped locomotives on the track. Each decoder will receive data packet addressed to it 15 to 20 times each second. This is important because in the absence of a packet bearing its address, a loco will continue doing what it was doing...indefinitely. If a packet of information is corrupted for some reason, it simply takes roughly a tenth of a second longer for the locomotive to respond to the change. Most people will be unable to tell that an error took place in such a short amount of time.