Automatic Brake Controller will generate asymmetric DCC to activate the braking feature on suitably equipped DCC decoders. ABC is fitted to Lenz silver/gold decoders, Zimo and many others. The DCC waveform is slightly modified by reducing the voltage on one side of the waveform by around 1.6 Volts. This activates the ABC feature on the DCC decoder (if present) and causes the locomotive to gently stop. When the circuit is deactivated the locomotive will gently accelerate. In its most simple form an ON/OFF switch is connected across the SWITCH terminals to activate the circuit.