E-STOP or Emergency Stop is a special speed step defined in the NMRA Digital Command Control Specifications.
For more information see the page on DCC Packets.
|C S3 S2 S1 S0||Speed|
Inside the DCC Packet is a set of bits reserved for speed step information. If all of the bits are set to a value of zero (0000 for 28 and 14 speed steps) the addressed decoder moves to the stop position.
If the Least Significant Bit (S0) is set to one (0001), the value is the E-Stop command. E-Stop is a Broadcast command, meaning that all decoders will immediately change to STOP and all moving trains halt.
By pressing the Emergency Stop button on your throttle the command station generates a broadcast packet with the E-Stop command and that is immediately transmitted to the booster and onto the rails. Everything in motion will immediately stop. The Standard states that the decoder shall immediately cease applying power to the motor.
The E-Stop command does not disconnect power to the rails. A valid DCC signal remains. Any multifunction decoders set to allow Analog operation could be set their locomotive in motion by a corrupted DCC signal, and may not respond to the E-Stop command.
* These commands are optional, and can be ignored for direction sensitive applications.
See the pages on Speed Steps and DCC Packets for more background on the NMRA DCC Standard.