Decoder programming is the act of changing CV values to meet specific operating characteristics.Decoder programming may sound a little challenging to some but for DCC decoders it is merely the act of changing the CV values to meet your desired operating characteristics. For instance; some may like long slow momentum settings which takes several seconds or even minutes to bring a model locomotive up to speed while others may desire a linear speed curve with instantaneous response. The beauty of DCC is that you can accomplish either or both of these responses for different locos. Most decoders come with pre-set CV values which are listed with the user’s guide for the particular device. Here are some of those values for one of my decoders. So! What is a CV? CV means Configuration Variable, a term selected as a standard for a decoder’s programmable memory location. CV1 for instance is the location where a locomotives short address, from 1 to 127 is stored. The extended or long address is stored in two locations CVs 17 and 18 and is used for loco numbers up to 9999. A CV will retain its value even when powered down but can be re-programmed at any time. A decoder with the pre-set values shown above will operate with linear speed response when locomotive address “3” is selected. This, of course, means a decoder can be installed and when wired correctly will operate as soon as the system is powered up. A nice feature with most decoders is the ability to re-set all CV’s to factory defaults. I have installed about 10 decoders in my steam engines and on several occasions have found some really weird responses to throttle commands ( such as—having an engine suddenly jump from a speed of 10 mph to 80 with a single step increase.) -An obvious example of a mistake in programming. The fastest remedy was to re-set all values to factory defaults and re-program. Decoder programming may look complicated and time-consuming the first time one attempts to work through all of the CVs, but the process becomes much simpler with experience. I keep a list of CV settings for each of my locomotives and the values for most of them have become easier to understand as I gain more knowledge about how they work. Not all decoders are the same and it is important to know what features and functions are available with a specific model. Here are some operating specifications for my above-mentioned decoder: When decoder programming for the first time it is necessary to use a separate programming track. Different DCC equipment suppliers normally have their own suggestions about the best procedure to use with their units. See your DCC system user’s manual for directions on how to program the CVs and the recommended layout of a decoder programming track section. If this is your first experience with DCC, it is a good idea to run your loco using the factory default values in order to become familiar with your throttle and how the system responds. When you are ready place the loco on the programming track and enter the program mode. The first decoder programming step is the address, CV-1 for primary address, or CV-17 and CV-18 for extended address. If the extended or long address is selected it is important to note that CV-29, the Configuration Register, must be set to enable the 4-digit address. Because of this the second step is to program CV-29. CV-29 the Configuration Register is the most important CV and controls the five characteristics shown below: 
The values for turning on the various switches are additive. For example; Our decoder programming example comes with CV-29 set to a value of “6”-which means switch 01=00 (NDOT forward selected), switch 02=02 (28/128 speed steps-ON), switch 03=04 (analog mode conversion on) switch 04=00 (speed table off), switch 05=00 (2 digit addressing selected). For a sum value of 6. For this setting only 2 digit address values (actually values up to 127) can be programmed. If we turned on 4 digit addressing, CV-29 would be “26”. When would one want to select NDOT(normal direction of travel) reverse? If two F series diesels were coupled with the lead engine in the forward position and the second engine in the backward position and they both had decoders, it would be necessary to use this selection for engine no. 2. CV-2 V-start: This is the additional voltage added to the drive voltage to overcome the inertia of the motor when the throttle is moved to the first speed step. The value is adjustable from 00 to 255 and each increment is an increase of roughly 0.5% of total motor voltage (that is-if you are using a linear throttle response curve! User-programmed and loadable speed tables have programmed speed values for each step and may not be linear.) Most of my locos have can motors and will move at a setting of 05 or less. This CV needs to be adjusted so that your loco will just begin to move. CV-3 Acceleration Rate: When a prototype locomotive engineer moves the throttle lever from stop up to the second or third notch the engine moves slowly at first and then begins to move a little faster in increments until it reaches the speed setting of the throttle. Adjusting CV-3 simulates this effect and has a range of values from 00 to 255. Setting CV-3 to 00 will result in an immediate speed response for each throttle speed step increase. The rate of speed change delay for each step is fastest at the low value settings and can be as much as several minutes at the higher values. Experiment with different values and set this effect with what appeals to you. CV-4 Deceleration Rate: The same momentum effect as CV-3 when the throttle is decreased in speed setting. The best setting for these effects is the one which seem the most realistic to the operator. CV-5 V-Max: This value sets the absolute maximum voltage to the locos motor at the highest speed setting. The range is from 00 to 255. A setting lower than 255 allows less than full voltage to be applied to the motor and limits the speed to a more realistic value. CV-5 is not available when loadable speed tables are used. CV-6 V-Mid: Sets the mid-point voltage to 50%. This value is normally set to 128 at speed step 15. CV-6 is not available when loadable speed tables are used. CV-17 and CV-18: These two CVs are used for extended or 4-digit address. Not all DCC systems support 4-digit addressing. Most of those that do have special methods for handling this type of addressing and it is not the same for different manufacturers. Follow the procedure as outlined in your decoder programming user’s manual for your particular model. Be sure to remember to set CV-29 for extended address or the decoder will only respond to primary address. CV-67 through CV-94: Loadable Speed Tables: If this feature is selected in CV-29 each speed value for our example decoder would be programmed by the user as shown below. Some decoders have pre-loaded speed tables which can be selected by the user but our example requires that each speed step must be loaded separately. 
This covers the main decoder programming features of our sample unit. Our decoder, like many others, has some additional features which we did not cover. There is one last CV that I would like to cover since I have used it often in my learning process. For our sample it is CV 8 or CV 30, Factory Reset, which requires a value of 2 to be entered and then a power down and restart to take effect. Sound decoders have more CVs that cover the generation of sound effects that are truly realistic and awesome. Most major DCC makers have websites where in-depth installation, operation, and technical downloads are available. Some of the sound folks even have their effects recorded for playback on line. Return from Decoder Programming to Digital Command Control Return from Decoder Programming to Home Page |
