Digitrax: Slot Management

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Summary: Managing the Slots of a Digitrax Command Station prevents unexpected issues during an Ops Session

Managing Slots

Releasing Individual Locomotives

A common reason for using all the slots in a command station is that locomotives are not properly dispatched when their operators are finished with them. To free a slot used by an individual locomotive, first make sure that the locomotive is removed from any consist that it may be part of. Then select the locomotive on a throttle, set the speed to zero, and dispatch the locomotive (see the throttle manual for instructions on how to dispatch locomotive addresses). This will set the slot to "free" and it can then be assigned to another locomotive when needed.

Continue this procedure for all locomotives that are occupying slots, but which not in use. (it may be difficult to determine which locomotive addresses are occupying slots in the command station)

Setting up the command station and Operator Discipline

  1. Purging makes a slot available for use. Purging requires the throttle be set to “0” (zero) speed and not be part of a UniVersal consist. Setting OpSw 14 to thrown and OpSw 15 to closed ensure all non-consisted individual addresses are purged.
  2. DCS 100/200 only: These command stations have 120 slots, however the factory default is 22 slots. Close OpSw 44 to make 120 slots available.
  3. Releasing or Dispatching: Ensuring each locomotive's throttle is at “0” (zero) speed and is either released or dispatched.
  4. Consists: “UniVersal” consisted locomotives (Digitrax's default method) will not be purged. Locomotives must be unlinked from their consist to allow these slots to be purged. This is an issue of Operator discipline. If you want permanent consists, consider basic or advanced consisting.
  5. Periodic OpSw 36 clear: Clearing the slots (OpSw 36) helps, especially if UniVersal consists are filling slots.
  6. If you reset OPSW 36 on your command station, all mobile decoder addresses and MU information will be cleared out of your Command Station. The manual that came with your command station will explain how to use the OPSW's (Op Switches). Note that this procedure will erase all consist information that is stored in the command station. (Universal Consists).

Advanced Slot Management

  1. Command Station Reset: Set to factory default by closing OpSw 39. CAUTION: This will clear the “Route Table’' (DCS 100/200) if in use. It will also clear the Alias Locomotive Roster (DCS 100/200). Alias Addressing requires a DT-100 throttle and is rarely used today.
  2. DCS100/DT200 Losing OpSw Settings: These command stations use a CR2032 coin cell to maintain their Random Access Memory which stores these and other parameters. If the cell is dead, all settings will be lost when the command station is shut down. Instructions for changing the cell are in the command station manual. The CR2032 cell and equivalents are commonly available. The command station requires one cell, there may be two cell holders, the empty one allows you to install a new cell before removing the old one, thus maintaining your settings. Do not install two cells as it is unnecessary.[1]

Command Stations


If a "slot=max" message appears on the throttle, the command station has no free slots available. With the DCS100, there are 22 slots available. Closing OpSw44 enables 120 slots. This means the DCS100 can control up to 22 locomotives at one time, or 120 if the additional slots are enabled.

Releasing locomotives which are not in use makes their slots available for use.

The DCS100 software has a purging strategy where any locomotive which has not been under the control of a throttle on LocoNet for 200 seconds will have its status changed from "in use" to "common", allowing anyone to acquire a locomotive which has been "forgotten" should that action be necessary (such as to avoid a collision.)

The DCS100's parameters allow you to lengthen the purge timing to 600 seconds, or to turn that feature off.


The DCS240 has 400 locomotive slots, and supports up to 400 throttles.

There are some differences:

  1. There are 120 standard slots which are available to any Digitrax throttle.
  2. The remaining 280 slots are considered expanded slots which are available to DT402 R2 and later super throttles. The DT402 R2 can be either tethered or Duplex versions. Throttles with expanded capabilities are assigned to expanded slots leaving the standard slots available for legacy throttles. The DCS240 identifies the throttles and assigns slots automatically based on their capabilities.


The DCS 50 and DCS 51 will display FuLL when the slots are full. The DCS 50 has only 10 slots, the DCS 51 (Zephyr Xtra) expands that to 20 slots.

Slots can be released by pressing the LOCO key and entering an address which is no longer in use, then EXIT. Clearing all slots and consists can be done by closing Option Switch 36 (DCS 50, DCS 52) (39 for the Xtra (DCS 51)).

A reset button on the rear of the DCS 52 (Express) will clear the slots when pressed.


When consisting, slots can be used quickly. Building a consist with a DT402/500/602 Super Throttle allows the DCS240 to store the entire consist in the expanded slots. The throttle only needs to address the primary (top) locomotive address in the consist to control the entire consist. If the consist is then selected using a legacy throttle, the primary address is moved to a standard slot, which is linked by the DCS240 to the remaining locomotives stored in the expanded slots, leaving as many of the first 120 "standard" slots available as possible.


What is Status FF?

Some users complain of getting a Status code of FF, and they cannot enter a new loco address into the system. The first question they ask is what is going on, there is no code FF? During operations, the display may say xFF or FuLL. This means the address space (slots) cannot accept a new address. During programming, FF or FuLL indicates there is too much load on the programmer, often caused by incandescent lamps.

Do not confuse Status Code FF with the returned CV value of FF on an service mode programmer like the Chief's or the PR1. These errors relate to programming decoders. During a Status check or Edit, you are dealing with the command station’s memory. When a programmer returns a CV value of 'FF', it indicates that it could not read back a valid CV value for this location in the decoder’s memory.

Further Reading


  1. Many erroneously refer to the memory in the command station as CMOS, and say they replaced the CMOS battery.