Firstly, your DCC command system should offer you the choice of speed steps. These are normally 14 (now almost not used), 28 and 128 (which actually is 126 steps!). By using the higher number of steps - 128 you will gain greater control over a loco speed and is ideal for shunting moves too. Therefore as a basic guide, 1 speed step in 28 step setting is equal to 10 steps in 128 setting = Much finer control in 128.
CVs are like 'tuning slots' in a decoder. You can "fine tune" a particular CVs Value to give optimum performance or make things happen in certain ways.
The most basic CV is CV1 which is the decoders address number. As a default its set to 3. You should normally set the address number to something else other than 3. Reason is that as you obtain more locos they too will (if new) be at address 3. Placing locos on the DCC tracks with the same address number will cause them to move together, which normally isn't what is wanted to happen.
Many decoders will have a setting range (called Value) of 0 to 63 or 0 to 256 or 255 Value range is depending on decoder manufacturer (There are other values too such as 0 to 512). Note; I reference a value of 0 (zero) a few decoders may actually start at a value of 1.
So setting a CV value to 0 (zero) will usually give maximum output for that CV and setting the value to the maximum number gives the lowest output.
CV2 is the setting used to allow the loco to just move from stationary at speed step 1 on the controller. It is therefore normally set to a very low value number.
CV3 is the Acceleration rate (e.g.Simulates a loco pulling away with a load) When set to 0 (zero) the loco will pull away immediately. Set the value to a higher number and the loco will take longer to go from stationary to the speed set by the controller.
CV4 is the deceleration rate. Set to 0 this will allow the loco to stop immediately the speed control is turned Off. Set the value to a higher number the longer it will take the loco to slow to a stop even when the speed knob has been off for some while.
CV5 is the Top speed which should be adjusted to give a realistic maximum speed of the loco. Higher values give lower top speed.
If your decoder supports CV6 then that value should be set to around one third to half the value set in CV5.
Finally, and for this exercise, most decoders will allow a factory reset to happen if CV8 is used. This when normally a value of 8 (CV8-8) is entered it will reset the whole decoder back to its as manufactured settings for all CVs and the address will become 3 again.
Whenever possible and your DCC system allows you to undertake CV reading. Read the value set in a specific CV and note it down BEFORE you begin to adjust that CVs value. When you have set a CV write down that value for future reference. You will never remember them!
