Accessory Decoders

Section Topics

1) What are Accessory Decoders?
2) Examples of Accessory Decoders
3) Features, Performance and Programming
4) Accessory Decoder Address Range
5) Accessory Decoder Control

1) What are Accessory Decoders?

The NMRA DCC standards define to type of DCC decoders.

1) Mobile Decoder
2) Stationary Decoder

A Stationary decoder goes by a far more common name of "Accessory Decoder".  We will use the term Accessory Decoder.

All DCC decoders have addresses allowing them to be controlled.  But Mobile Decoders addresses are not the same as Accessory Decoders by design.  They do not overlap or interfere with each other.  Technically it is type of address that ultimately defines a given decoder as a Mobile or Accessory Decoder.

Mobile decoder are decoders the are used in rolling stock that run on the track.  The DCC addresses are typically assigned by the user to be the engine number itself.  Using that address, you can control motor speed, lights and sound.  Mobile engine decoders are specifically designed to control engines.

Accessory decoders are decoders used to control devices that do NOT role down the track.  The DCC addresses are also assigned by the user and required one to document as to what they are going to control.   Accessory decoders are specifically designed to control many different types of accessory devices such as those listed in the next section.

2) Examples of Accessory Decoders

1) Switch Machines.  (Slow motor or Twin coil types)
2) Signals. (Target, 2/3 light, position, semaphore)
3) Scenic Backgroung Layout Lighting. (NCE has such a system and in only sold directly by NCE.)
4) Scenic Light Effects.  (Chasing lights, random flicker, blinking.)
5) Control panel indicators.  (CTC board implementation) 
4) Layout Animation. (Run trains, do special effects in lights or sound.)

Switch Machine Accessory Decoders
NCE Switch-Kat
Lenz LS150
NCE Snap it Rev B

3) Features, Performance and Programming

There is no NMRA electrical performance standard or requirement for decoder outputs.  However, by the nature of their function, they are designed to control specific types of loads.  This is indicated on the front page of the Accessory Decoder manual.  There should be application specific electrical specifications included along with discussion of the supported input power source options you have.  Some may have options you program into the Accessory Decoder to enable or disable features or functions as required.  Just like a Locomotive Decoder, programming can be done using the programming track or "Operation Mode" (OPS MODE) or "Programming On the Main" (POM).  However, only one or the two methods are supported BUT by far and away OPS mode is used since in permits programming at the installation point as opposed to back at the programming track location.

4) Accessory Decoder Address Range

Address range is: 1 to 2048.

Just like a locomotive, an Accessory Decoder requires a DCC address.  
Per the NMRA DCC standards, Accessory Decoder Addresses 
DO NOT overlap nor are shared with Engine Decoder Addresses and visa versa.  These two address ranges have nothing to do with each other.  Simply put, there is nothing to worry about here.

5) Accessory Decoder Control

There are two way to control an accessory Decoder.

1) Manual (Local) using buttons.

If the decoder supports it, local push button or switch control inputs can activate the accessory output.  The support varies with the type and purpose of the accessory decoder.

2) DCC Command
By sending command to these devices, you can throw a switch, set a signal aspect or do anything you want provided it is electrically controlled or powered.  There are two types of accessory decoder command formats:

a) Simple: On or OFF.  (Throw a turnout to reverse or normal positions.    Turn a light on or off.)
b) Complex:  8 Bits.  (This is currently not a NMRA approved format to date.  Can be used to control light intensity or signal aspects.)

As to which type is used will depend on the type of accessory decoder you have.  But by far most use the SIMPLE format.