Bushby Bit

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Summary: The Bushby Bit is a software switch found in Digitrax command stations. It prevents turnout changes via the throttle, giving control to the dispatcher or Central Traffic Control.

Purpose

The Bushby Bit removes the ability to control turnouts from the throttle and assigns that task to a dispatcher. As turnout commands are also used for signalling purposes, it adds a new level of automation possibilities.

When activated, it disables control of turnouts (switches) by the throttle. It is OpSw27 (default is "t" for thrown) in the command station options. It allows control of the turnouts via LocoNet using an attached computer and software. An example would be CTC (Central Traffic Control) where the train crew only operates the train, according to the signals.

Only the throttles are affected. Accessory decoders with external switches are not affected. If an operator cannot control the turnouts from his throttle, the Bushby Bit is probably the cause (OpSw27 = closed). See your user manual to find the procedure to change option switches in the command station.

It is also possible to set/view the option switches using a LocoBuffer and JMRI connected to your LocoNet.

More info on the Digitrax Website: Bushby Bit

Implementation

LocoNet has two types of control messages available for turnout control. These will be described as Normal and Alternate messages. These messages can also be used for signalling purposes.

When a LocoNet device such as a throttle creates a turnout command, it uses a specific message format. This message is forwarded via LocoNet to the command station. The command station interprets the message, formatting it into an accessory decoder packet. This is transmitted via the RailSync signals to the booster(s).

In the default state, where the Bushby Bit is inactive, the command station will buffer both types of messages, prior to processing them into accessory decoder packets.

A computer on LocoNet can be used to intercept the turnout messages from the throttles, then create a new one in the alternate format. This alternate message is then forwarded via LocoNet to the command station.

When the Bushby Bit is enabled (OpSw27="C"losed), the command station only buffers the computer generated Alternate LocoNet switch control messages, ignoring those from the throttle. Accessory decoder packets will not appear in the RailSync signals. As RailSync is the reference signal for boosters, it will not appear on the track either. This prevents accessory decoders connected to the power bus from acting on turnout instructions as they will not receive those messages in an accessory decoder packet.

Software can then take control of the turnouts, sending alternate messages via LocoNet to the command station, which now ignores turnout messages from a throttle. This allows for dispatcher control as well as route and signal automation.

If enabled, devices using the RailSync signals on LocoNet will be affected. Some LocoNet devices, such as the SEC8, can be configured to use either RailSync or the higher power LocoNet signals.

Accessory decoders such as the DS64 and DS74 have the option of using the alternate message format present on LocoNet. The DS54 cannot as its LocoNet connection is used for reporting only.

Origins

In 1994, Strad Bushby developed a method to control which commands would be executed in a digital command control system by setting what became known as the “Bushby Bit”. When set, commands sent to the layout from computer programs would be directed to a specific program, which reformatted and forwarded the command to the layout. He would set up a network of computers connected to his layout and DCC system. Digitax added the Bushby Bit to certain command stations to enable modellers to use computers to control signals and turnouts, leaving the engineer to run the train while a dispatcher controlled the routes. When set, the throttle cannot control turnouts.

(Taken in part from Exhibit A, JMRI s. Katzner, 174-2.PDF

References

  1. JMRI Turnout Control Handling
  2. Bushby Bit discussion on GroupIO