That's a function some ESU decoders have - to do the "Kadee Shuffle" at the press of a function button. Maybe some other decoders have this as well.
Or maybe you are thinking of the brake function on the decoder. Some decoders implement it in a way that even witht he throttle on say 25%, you can use the brake function to stop the loco, and when you release the brake it gradually returns to the throttle speed.
Or the switching function built in to several decoders, which when that function button is activated, it cuts the top speed of the loco by 50%, as well as cutting any momentum you might have set on the decoder in half.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
I have a Digitrax starter kit from two years ago with the DT500 throttle. Used it lightly while laying track and test run a new Broadway Limited N scale SD40-2. Some time has passed and getting rolling stock back on layout since major scenery done. Maybe I was dreaming but thought there was a pause button that held the loco in place then released it back to where throttle was for uncoupling instead of throttling down then back up or using the E stop then throttle back up. Thanks