CV61 Make sure you read all the way through for proper understanding!!!
The NMRA has specified the purpose for all current CVs. There are a limited numbers of CVs that may be used by manufactures for their own specific features. Because of this, we combined several different features into this one manufacturer defined CV (CV61). CV61 controls Back EMF, Rule 17 dimming options (dim when stopped) and opposite dim control. For information on Rule 17 dimming read HERE. For information on opposite dim control read HERE For information on Back EMF please read HERE.
While CV61 is often found to be difficult and easily misunderstood, the overall concept is rather simple. Each feature in CV61 has a number, if that number is entered into CV61 then the feature will be active. If the numbers for different features are added together, then those features will be active.
So, here is the list of features and their corresponding numbers. If you want BEMF turned off you need a value of zero. If you want BEMF turned on you need a value of one. If you do not want to be able to control BEMF with a button (BEMF is automatic) you need a value of zero. If you want control of BEMF with a function button you need a value of two. If you do not want the dim when stopped Rule 17 feature, you need a value of zero. If you want the dim when stopped Rule 17 feature, you need a value of 16 If you do not want the opposite dim feature you need a value of zero. If you want the opposite dim feature you need a value of 32.
Then you simply have to add all the values for all the features that you desire and all of them will be active. If you are familiar with CV 29 this procedure is very similar.
CV61 = 1 (BEMF turned On) CV61 = 0 ( BEMF turned Off) CV61 = 16 (Dimmed when Stopped) CV61 = 17 ( 16+1 so BEMF turned On, Dimmed when stopped) CV61 = 32 (Opposite light dimmed) CV61 = 49 (32+16+1 so BEMF is On, Dimmed when stopped is On, and Opposite dimming On)

I have a locomotive sitting on the programming track and when I read CV61 I got a value of 34. What does it mean?
When reading the value of CV61 on the programming track, you start with the feature that requires the largest value (opposite light is dimmed = 32). If this number can be subtracted from the value currently in CV 61, then do so and continue to the feature with the next largest value. Because the value for this example is 34 we can see that 32 (opposite dim) can be subtracted and therefore is active, so we do 34 – 32 = 2. The next largest value is 16 (Rule 17). This is not active because it cannot be subtracted from 2. The next value is 2 (button controlled Back EMF) so this feature is turned On. We now subtract 2 -2 and see that BEMF is disabled because there is only zero left. Because of the fact that BEMF is turned Off, the value of 2, which allows you to control BEMF with the button, will not be active, because whether the button is pressed or not BEMF is still off. In order to turn BEMF On while maintaining the other features add a value of 1 . So the original value of 34 would become 35.