usually also a transition section to prevent short circuits. An electronic control module is switched when the signal changes to danger and changes the track voltage in the stopping area. Märklin Digital (new) In 1993 an enhancement to the original system introduced improvements for locomotive control: Additional four switched functions F1 - F4 Absolute direction control with direction sent as part of speed commands The changes were entirely compatible with earlier locomotive decoders so any controller was able to control any locomotive decoder type (a few special function decoders developed earlier were incompatible with the revised protocol, 6021 control units could be set to send old protocol only). Absolute direction control is important for computer controlled layouts so that, after power off, locomotives will restart in the previously controlled direction. Older c90 decoder equipped locomotives will always restart forwards after power off, regardless of the previously controlled direction. Controllers The new 6021 combined control unit & locomotive control with additional function buttons. Miniature switches set the operating mode (old or new protocol) and reduced track voltage for shunting areas. The new Control 80f allowed additional locomotive controllers to be plugged into the right hand side of a 6021, other modules as before. Decoders 1997 c91 (60901) decoders provided additional function outputs F1 - F4, 27 speed steps (stop 0 and 1 - 27), and improved motor regulation. Although the new decoders had 27 speed steps, existing controllers could only send 14 and so the decoders would step up odd steps and down even steps making all 27 steps accessible. The extra functions allowed for other features such as additional lighting and sound. While the small size of speaker that can be fitted into H0 locomotives limits reproduction, built in sound has become a feature of many models. Adjustments to the new decoders required tools, as before. "Function" was most commonly used for locomotive headlights, F1 & F2 were usually used for other power functions such as smoke units or additional lighting. F3, when available, was commonly used for sound, and F4 usually used to disable artificial inertia for precise control, especially when shunting. These decoders are now designated "fx" to distinguish them from earlier decoders lacking additional switched functions. Function decoders Function decoders without motor control can also be fitted to carriages providing the 5 switched functions to control train lighting and other additional features. They may also be fitted