The Why? and How?

STOPPING!!
When operating a DCC layout, any locomotive with a DCC decoder can be slowed to a stop by several different methods.
The "Engineer" can send a CAB command to reduce speed.
When the layout is controlled by a PC and software an
occupancy detection device can send a
"BRAKE"
command to specific engine address.
OR
Depending on the decoder "Braking" can be initiated with simple BitSwitches via one of 3 different methods.

1. Track power can be switched to analog DC
           Most NMRA conformance decoders and LGB MTS
2. A universal "Set Speed Zero" packet can be broadcast to the section.
           Most NMRA conformance decoders and LGB MTS
3. The DCC signal can be altered to an Asymmetric Signal
          (Lenz Gold Decoders, Zimo, Umelec)

In any case the engine  will begin to stop and apply the braking momentum value stored in CV4 of the engine's decoder .  When a "GO" is restored to the rails the engine will begin to accelerate by applying the acceleration momentum value CV3 stored in the affected engine's decoder.

Automatic braking at a signal can also be accomplished an occupancy detector when a "BitSwitch" is installed.

The
"Timed Stop BitSwitch"
is one example

When the train activates the track contact (reed switch or any sensor that can close a circuit) the DCC bit packets to the isolated section of track are interrupted for 0 to 120 seconds depending on the time set.  The train will slow to a stop using the braking momentum stored in CV4 of  that engine's decoder. When the set time elapses the engine will accelerate to it's preset speed using the acceleration momentum value set in CV3.

Similar schemes are used for other BitSwitch products.

"DCC Made Easy"     $11.50
kalmbach publishing

This publication is a must for an introduction to DCC and includes: