Technical Reference for Throttle Developers

This page is intended to capture relevant information to assist those who develop throttles compatible with EX‑CommandStation using the DCC-EX Native Protocol, not the WiThrottle protocol.

This page should be read in conjunction with the DCC-EX Native API Reference in order to understand how to send and parse DCC-EX API commands correctly, and ignore any irrelevant commands.

Considerations for throttle developers 

For anyone developing a throttle or controller application, these considerations should be taken into account:

Refer to the DCC-EX Native API Reference
Refer to the DCC-EX Native Commands - Consolidated Reference
A throttle/controller MUST accept and ignore anything it does not understand
Track power state has three possible states: On, Off, and Unknown
There is no concept of a throttle ‘acquiring’ a loco.
Simply, commands for a loco are sent to the Command Station, and the Command Station ‘broadcasts’ the status of any/every loco to every throttle any time a change is made to a loco.
There is no concept of the throttle disconnecting from the Command Station.

Responding to appropriate information 

In addition to understanding the specific throttle commands details on this page, throttles/controllers also must understand and respond appropriately to broadcasts sent from the DCC-EX API.

These are the key broadcast responses that should be understood:

<p X [MAIN|PROG|JOIN]> - When a throttle issues a track power command, this response is sent as a broadcast (see Power Management)
<r address> - When a loco address is read on the programming track, the address is sent as a broadcast (see Reading/Writing Configuration Variables (CVs) - Programming track)
<l cab slot speed/dir func> - When throttles send loco commands, this is sent as a broadcast (see Cab (Loco) Commands)

These broadcast responses should be understood if your controller deals with turnouts/points and sensors. - <H id [DCC|SERVO|VPIN|LCN] ... [0|1]> - When turnouts are closed/thrown, this response is broadcast (see Turnouts/Points) - <[q|Q] id> - When sensors are deactivated/activated, this response is broadcast (see Sensors)

This feature is not available in the current 'Production' version

There are now turntable/traverser <i id position moving> broadcast responses if the new turntable/traverser objects are implemented (see Turntables/Traversers).

Working with track power states 

Track power can be On, Off, or Unknown. There is no broadcast of an Unknown power state though, meaning a throttle/controller must start with track power flagged as Unknown.

The throttle should only flag the power state as On or Off when either:

A power broadcast is received from the EX‑CommandStation <p...>
The throttle user selects to turn track power on or off

Key Throttle commands 

Key throttle specific commands are summarised here, refer below for elaboration on the details with examples. Refer to the DCC-EX Native Commands - Consolidated Reference for detailed information.

Command	Response	Description
`<t cabid speed dir>`	`<l cabid slot speedbyte functionMap>` (Broadcast)	Sets a cab (loco) speed and direction. (See below for the response)
`<t cabid>`	`<l cabid slot speedbyte functionMap>` (Broadcast)	Requests a deliberate update of cab (loco) speed/functions
`<F cab funct state>`	`<l cabid slot speedbyte functionMap>` (Broadcast)	Turns cab (loco) decoder functions ON and OFF (See below for the response.)
`<JT>`	`<jT id1 id2 id3 ...>`	Returns the defined turnout IDs
`<JT id>`	`<jT id state "[description]">`	Returns the ID, state, and description of the specified turnout ID
`<JA>`	`<jA id1 id2 id3 ...>`	Returns the defined automation and route IDs
`<JA id>`	`<jA id type "[description]">`	Returns the ID, type (A=automation or R=route), and description of the specified automation/route ID
`<JR>`	`<jR id1 id2 id3 ...>`	Returns the defined roster entry IDs
`<JR id>`	`<jR id "description" "function1/function2/function3/...">`	Returns the ID, description, and function map of the specified roster entry ID
`<JO>`	`<jO id1 id2 id3 ...>`	Returns the defined turntable IDs
`<JO id>`	`<jO id type position position_count "[description]">`	Returns the ID, type (0=DCC or 1=EXTT), current position, position count, and description of the specified turntable ID
`<JP id>`	`<jP id index angle "[description]">`	Returns the turntable ID, position index, angle, and description of each defined position for the specified turntable ID

Additional Details 

Refer to the DCC-EX Native Commands - Consolidated Reference for detailed information on these commands.

Setting cab (loco) status 

<t cabid speed dir> - Sets a cab (loco) speed and direction. (See below for the response.)

<F cab funct state> - Turns cab (loco) decoder functions ON and OFF. (See below for the response.)

Obtaining loco (cab) status 

<t cabid> - Requests a deliberate update on the cab speed/functions in the same format as the cab broadcast.

Example response:

<l cabid slot speedbyte functionMap> - Note that a slot of -1 indicates that the cab is not in the reminders table and this command will not reserve a slot until such time as the cab is throttled.

Where:

cabid = Loco’s DCC address

slot = Position in the reminders table (for the convenience of slot managers later)

speedbyte = The DCC packet speed bye including the direction bit (NOT the same as the DCC-EX speed)

reverse - 2-127 = speed 1-126, 0 = stop

forward - 130-255 = speed 1-126, 128 = stop

functionMap = Binary map of which functions are ON ( 1=F0, 2=F1, 3=F0&F1 etc.)

The above is not a direct response, but rather as a broadcast that will be triggered as a result of any throttle command being issued by any device for the cab(loc) in question.

Turnouts/Points 

The conventional turnout definition commands and the <H> responses do not contain information about the turnout description which may have been provided in an EX-RAIL script. A turnout description is much more user friendly than the identifier (eg. T123), and having a list helps the throttle UI build a suitable set of buttons.

<JT> - Returns a list of turnout IDs. The throttle should be uninterested in the turnout technology used but needs to know the IDs it can throw/close and monitor the current state.

Example response:

<jT 1 17 22 19> - Turnout IDS 1, 17, 22, and 19 are defined.

<JT 17> - Returns the description for turnout ID 17, and the status of T=thrown or C=closed.

Example responses:

<jT 17 T "Coal yard exit"> - Description “Coal yard exit” plus state is thrown.

<jT 17 C "Coal yard exit"> - Description “Coal yard exit” plus state is closed.

<jT 17 C ""> - Indicates turnout description not defined, and state is closed.

<jT 17 X> - Indicates turnout unknown (or possibly hidden.)

Note

It is still the throttles responsibility to monitor the status broadcasts. Also note that turnouts marked in EX-RAIL with the HIDDEN keyword instead of a “description” will NOT show up in these commands.

Note

Note from the author: The existing broadcast is messy and needs cleaning up, however, I’m not keen on dynamically created/deleted turnouts so I have no intention of providing a command that indicates the turnout list has been updated since the throttle started. - Chris Harlow

Automations/Routes 

A throttle needs to know which EX-RAIL Automations and Routes it can show the user.

<JA> - Returns a list of Automations/Routes.

Example response:

<jA 13 16 23> - Indicates route/automation ids 13, 16, and 23 are defined.

<JA 13> - Returns information for route/automation ID 13 including the description, and if it is a route (R) or automation (A).

Example responses:

<jA 13 R "description"> - Returns the description for ID 13, and that it is a route.

<jA 13 A "description"> - Returns the description for ID 13, and that it is an automation.

<jA 13 X> - Indicates ID 13 is not found.

What’s the difference?

A ROUTE is just a call to an EX-RAIL ROUTE, traditionally to set some turnouts or signals but can be used to perform any kind of EX-RAIL function, but is not expecting to know the loco ID.

A route can be triggered by sending, for example, </START 13>.

An AUTOMATION is a handoff of the last accessed loco ID to an EX-RAIL AUTOMATION which would typically drive the loco away.

An automation expects a start command with a cab ID, for example </START 13 3>.

Roster Information 

<JR> - Requests a list of cab IDs from the roster.

Example responses:

<jR 3 200 6336> - Returns the roster entry IDs 3, 200, and 6336 are defined.

<jR> - Indicates no roster entries are defined.

<JR 200> - Returns the roster name function map for roster ID 200.

Example response:

<jR 200 "Thomas" "whistle/*bell/squeal/panic"> - Returns the defined description “Thomas” with each defined function’s name. Refer to the EX-RAIL ROSTER command for function map format.

Turntables/Traversers 

This feature is not available in the current 'Production' version

A new feature has been added to support control of turntables/traversers from throttles, including the ability for throttles to “draw” turntable positions as defined to support graphical operation. If EX‑RAIL commands are used to define turntables and their associated positions, a description for the turntable as well as each position is able to be defined.

Note that to obtain a complete definition for a turntable/traverser, the turntable object needs to be queried first (<JO id>) followed by the position query (<JP id>) to obtain all defined positions for the object.

<JO> - Returns a list of turntable IDs.

Example response:

<jT 1 2> - Turnable IDs 1 and 2 are defined.

<JO 1> - Returns details of turntable ID 1.

Example responses:

<jO 1 0 1 5 "DCC Turntable"> - DCC turntable type currently at position 1, with 5 defined positions and a description “DCC Turntable”.

<jO 1 1 0 11 "EX-Turntable"> - EX-Turntable type currently at the home position (0), with 11 defined positions and a description “EX-Turntable”

<JP 1> - Returns all positions for turntable ID 1.

Example responses (will return all positions):

<jP 1 0 0 ""> - Position 0, unused for DCC turntables, “home” for EX-Turntable

<jP 1 1 100 "Turntable position 1"> - Position 1, 10 degrees from home

<jP 1 2 1800 "Turntable position 2"> - Position 2, 180 degrees from home

Commands to avoid 

<f cab func1 func2> - Use <F cab function 1/0> instead
<t slot cab speed dir> - Just drop the slot number
<T commands> - other than <T id 0/1>
<D> - If the throttle developer sees the need to obtain info which is <D> only please contact us to get a better way to do it