How Does Digital Command Control Work
How Does Digital Command Control Work?
- Main article: DCC Power
Though it can sometimes be useful to understand how an underlying technology works, it is usually not necessary to understand a technology for one to use it. Most of us use the Internet without understanding the underlying TCP/IP protocol suite. Likewise, there is no need to understand the technology behind DCC in order to use it. The information below is provided for those who wish to understand DCC's underlying technology.
|Is It AC or DC?|
The most frequently asked questions about Digital Command Control are "Is the Digital Command Control waveform applied to my track AC or DC?" and "Is it a special form of AC?"
The answer is: No.
Many of those ideas come from trying to apply analog ideas and what is in a wall outlet to a digital signal.
Clear Your Mind
Approach Digital Command Control with an open mind. As a Digital technology, avoid thinking in analog terms. Many myths have arisen over the years, often by trying to fit Digital Command Control into an analog concept, or by those who fear Digital Command Control. There are many out there who will try to apply analog concepts to digital. It just does not work that way. Most problems related to Digital Command Control exist not with the technology but within the user's frame of reference.
Conceptually, How Does DCC Work?
DCC works by conveying operating commands, such as speed and direction, to the locomotives via modulation of the track "signal". Each locomotive has at least one pre-assigned address. Since Commands are part of the track signal, all locomotives receive them, but each locomotive only acts on commands addressed to it. All other locomotives ignore the command. (There are some exceptions, like "all stop") To ensure reception of commands, typically commands are repeated periodically. DCC commands are broadcast at more than a hundred commands per second, so each locomotive receives its command updates in a timely manner.
Electrically, How Does DCC Work?
Digital Command Control signals are encoded into the voltage applied to the track (10 to 24 volts, depending on scale (per the NMRA standard). One of the very smart ideas about this is that with a full wave bridge (or diode matrix in this application), very little filtering is needed to turn this source of power into DC to operate the decoder and the motor. The sinusoidal AC in your home needs a lot of filtering to make "good" DC. Thus the DC needed to power the microprocessor in your decoders can be done simply and compactly.
What are DCC Packets?
As stated earlier, the decoder interprets the modulated signal as "ones" and "zeros", or bits. Eight bits form a byte. Commands are made of these bytes. The command station sssembles these bytes of data into a packet. A packet is a complete DCC command, with the preamble, address, commands and error correction bytes. Packet sizes can vary slightly, so 100 to 200 packets are broadcast per second.
Operationally, How Does DCC Work?
The following links have examples of how to accomplish a move using a DCC system.
Operational Example: Moving a Locomotive
- Main article: Introduction to DCC/Moving a Locomotive
Operational Example: Moving a Locomotive Onto a Siding
- Main article: Introduction to DCC/Moving a Locomotive Onto a Siding