Deceleration is the rate at which the decoder decreases from one speed step to the next in response to a new command to decrease speed.
CV04, deceleration, lets you simulate locomotive braking action. The range of values for CV04, deceleration, is 000 to 031 (x00 to x1F hex). A value of 00 causes an immediate response to a new command to decrease speed. As you increase the CV value programmed into CV04, the rate of speed step change is approximately 1/10 second per increment in deceleration value.
For example a value of 01 programmed to CV04 causes the decoder to change at 1/10 second per speed step (using the 28 speed step range). This means that it would take 2.8 seconds to decelerate from full speed to stop if you commanded the loco to go immediately to stop when it was moving at full speed.
Caution: If acceleration and/or deceleration are set at a high value, the loco may not appear to be working correctly. If your loco is not responding when you increase or decrease your throttle setting, reprogram these two CVs to 00 and try again.