Command Stations are the very heart of the Digital Command Control system. They receive commands from a throttle network (such as Digitrax's Loconet or Lenz's ExpressNet), process them, and decide if it needs to make a standardized DCC packet to send to the decoders on a Digital Command Control system. They don't do the actual work; they tell other things to do the work. The digital data packet is sent to the Booster, which creates the DCC signal imposed on the track.
What is a Command Station?
In the early days of DCC, the command station was its own entity. Two components were required: a command station and a booster. The throttle network connected to the command station, the output of the command station was connected to the booster. The booster's output was connected to the track. In the mid 1990s a small company called RamFixx Technologies introduced their revolutionary RamTraxx DCC system featuring the command station and booster combined into one unit. Combining both units into a single package reduced the cost by about 20%. Many people refer to the integrated device as the command station.
Your layout only needs one command station. It can have multiple boosters. Avoid using a command station in booster mode whenever possible, should it come online as a command station there will be problems. Dedicated boosters are a better option when multiple boosters are needed. Older command stations with program outputs can always be repurposed to a dedicated program track.
Another type incorporates not only the command station and booster, but includes the throttle within the same unit, such as the Digitrax Zephyr system. CVP's EasyDCC command station has the throttle and command station in the same package, but requires an external booster such as their ZoneMaster. Many entry level DCC systems use this approach.
Purpose of the Command Station
The command station listens for commands from throttles and other devices, processes them, sending the resulting instructions to the booster. The booster amplifies the digital data stream from the command station to the required voltage. The resulting output is a completely digital signal which is applied to the track. On the track are locomotives, with their multifunction decoders. Other accessory decoders, controlling turnout motors and crossing gates, may also be connected to the track to receive commands.
The command station can be 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 interpreting additional functions sent by the throttle.
For example, if your command station supports 2 digit addresses only, your decoders will only see 2-digit addresses on the track, even though the decoder is capable of understanding a four-digit address. (These are hexadecimal, not decimal numbers. The actual range of addresses available are determined by the software in the command station). Some budget oriented DCC Starter Sets may limit the total available addresses to 10. The same applies to features like speed steps, consisting, and the maximum number of locomotives which can be controlled by the command station.
As a rule, any limitations of the command station must be identified on the packaging so the buyer can make an informed decision.
Command stations vary from manufacturer to manufacturer, offering different levels of features. Differences may include the amount of memory allocated (or slots in a Digitrax system) for running trains, range of functions supported, upgrade or expansion possibilities, output current (expressed in amperes) available to the track and the total 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 offered by various vendors are incompatible with other brands.
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:
Example: Ten 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.
The software in the command station can optimize transmission rates, by prioritizing packets. This minimizes lag when a large number of locomotives need to be handled in a timely manner. Addresses with no change in status are transmitted less frequently so that addresses with changing data can be handled quickly. For example, a mainline freight with the highball compared to a shunting engine, one has little changes to the throttle, the other has many.
The command station is the center of the throttle network. This network connects both throttles and boosters, as well as other accessories, to the command station. There are different types of throttle networks, depending on the manufacturer. This means that one brand of DCC equipment will not be compatible with another, due to differences in the throttle network.
- The type of throttle network has no impact on the interoperability of decoders on the track. The NMRA DCC standards apply to the DCC signals on the track only, and do not include throttle networks.