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Mnemonic Quick Reference

Note To Editors

Please take a look at the PowerOutage and OutOfService pages and try to maintain the same format on new pages for consistency. I'm open to suggestions If the format needs to be adjusted/expanded -- I just want to try and keep it consistent looking through out the pages.

Mnemonic Formatting

Base Mnemonics and Controls Vs. Indications

Listed below are the "Base Mnemonics" that make up the various logic functions that drive ATCS Monitor. We try and use the same base mnemonics that the industry uses to label wires, relays, etc. The base mnemonics must be put in either a Control or Indication format before they are actually useful by the application; visit the DecodingMnemonics tutorial for guidance on how to assign mnemonics to the default K## or C## values broadcast by an undecoded MCP.

Indication bits (those from an MCP) end with a K, and Control bits (originating from a BCP) end with a Z. For instance, EG is the base mnemonic for an EastboundProceed ( Eastbound Green) signal. A request from the dispatcher for an EastboundProceed signal would be EGZ (transmitted from a BCP to an MCP). The mnemonic to indicate that the aspect is displayed in the field is an EGK (transmitted from an MCP to a BCP).

Multi-Mnemonic Labeling Techniques

You will often see numbers and letters before mnemonics for multiple tracks and interlockings. For example 1WAK would indicate the WestboundApproach block occupied on main one (for instance), and a 2WAK would indicate the WestboundApproach block occupied on main two. You can use 0-9, and A-Z to identify these multiple instances. There are no rules within the program that dictate when you should use a 1WAK verses a 2WAK, so long as it matches what you want displayed in TrackBuilder. However, let logic be your guide -- it wouldn't make much sense to label mnemonics for track two as 1xxZ and 1xxK, and for track one as 2xxZ and 2xxK; similarly for a plant with multiple switches, for switch no. 1 use 1xWZ and 1xWK and for switch no. 2 use 2xWZ and 2xWK.

Inverted Mnemonics

In rare instances, there may be mnemonics transmitted where the logic is inverted. This means that when the bit goes high (or "on"), the condition is false, and when the bit goes low (or "off"), the condition is true. These mnemonics are put into the Mnemonic Maintenance dialog in lower case letters to indicate that they are inverted. For example, Bridge 37.0 on BNSF's Bellingham Subdivision does not transmit bits indicating the drawbridge seats, wedges and easer bars are engaged, and does transmit those bits when the bridge is open. Thus, the mnemonics would be entered in the form cwedgesk instead of CWEDGESK to ensure proper display of the active text denoting these elements.


This sample, based on two CSX Philadelphia Subdivision control points, shows component nomenclature:


The control point at E Feltonville has two main tracks and two sets of crossovers. The control point at Chester has two main tracks to the West and a single main to the East, and has a single switch. Both control points "own" their approach blocks on all tracks.

Note that some component names are duplicated on the diagram and that some mnemonics are associated with multiple components.

Component Name Location Description Associated Mnemonic(s)
A:1EA E Feltonville track 1 East approach 1EAK
A:1EG E Feltonville track 1 Eastbound absolute signal 1EGK, 1TEK, 1EGZ, 1STZ
A:1NW E Feltonville crossover no. 1 (both switches) 1NWK, 1RWK, 1NWZ, 1RWZ
A:1T E Feltonville track 1 in plant (within interlocking limits) 1TK
A:1WA E Feltonville track 1 West approach 1WAK
A:1WG E Feltonville track 1 Westbound absolute signal 1WGK, 1TEK, 1WGZ, 1STZ
A:2EA E Feltonville track 2 East approach 2EAK
A:2EG E Feltonville track 2 Eastbound absolute signal 2EGK, 2TEK, 2EGZ, 2STZ
A:2NW E Feltonville crossover no. 2 (both switches) 2NWK, 2RWK, 2NWZ, 2RWZ
A:2T E Feltonville track 2 in plant (within interlocking limits) 2TK
A:2WA E Feltonville track 2 West approach 2WAK
A:2WG E Feltonville track 2 Westbound absolute signal 2WGK, 2TEK, 2WGZ, 2STZ
B:1WA Chester track 1 West approach 1WAK
B:2WA Chester track 2 West approach 2WAK
B:EA Chester single track East approach EAK
B:EG/NW Chester Eastbound absolute signal when switch normal NWK, RWK, NWZ, RWZ
B:EG/RW Chester Eastbound absolute signal when switch reversed EGK, TEK, EGZ, STZ
B:NW Chester switch NWK, RWK, NWZ, RWZ
B:T Chester track in plant (within interlocking limits) TK
B:WG Chester Westbound absolute signal WGK, TEK, WGZ, STZ

List Of Mnemonics

The Mnemonics in bold below are officially supported by ATCS Monitor. This means that they are part of the core functionality making the dispatchers display work.

Those not in bold can all be used within ATCSMon, however, there is no "built in" support for them to do anything on the dispatchers display. If desired, you will need to add that support using ActiveText or LayoutScripting with VBScript. These mnemonics are commonly used among ATCS Monitor users and often map to actual signal design charts, but vary.

Each exists in the layout as is, preceded with <station call-up="call-up" letter="letter">:x, e.g. F:1WA (where 1 is optional).

Each exists in the mnemonic maintenance dialog appended with a K for MCP indication bit or Z for control bit (note that there are no controls for approach or plant occupancy bits), and optionally preceded with a letter or number.

Block Occupancy

(see the discussion on geographic versus bounded approach naming here)

  • WA - WestApproachTrack or WestboundApproach
  • EA - EastApproachTrack or EastboundApproach
  • NA - NorthApproachTrack or NorthboundApproach
  • SA - SouthApproachTrack or SouthboundApproach
  • LA - LeftApproach - Layout direction alternate to a compass direction
  • RA - RightApproach - Layout direction alternate to a compass direction
  • *O* - OrOccupancy - Works like a logical OR to indicate approach block occupancy.
  • *B* - BlockOccupancy - Works like a logical AND to indicate approach block occupancy.
  • *X* - OutOfService - Replace the "A" in the approach block with an X.
  • *T* - PlantOccupancy - Indicates interlocking occupancy of the control point.
  • Dead - DeadBlock - A non-bonded block, not under ATCS control (greyed out on display). Used in TrackBuilder.

Switch, Turnouts, and other Track related

  • BRDN - BridgeDown
  • BRUP - BridgeUp
  • LZ - SwitchLock
  • NW - NormalSwitchAlignment
  • RW - ReverseSwitchAlignment
  • UL - SwitchUnlocked
  • L - RouteLock (may use LZ in place of)


  • EG - EastboundProceed
  • WG - WestboundProceed
  • NG - NorthboundProceed
  • SG - SouthboundProceed
  • ST - SignalStopControl - Instruction to set signals to stop
  • C0 - CallOn (defined C-ZERO in ATCSmon, not the letter "O", see OrOccupancy) - Allows dispatcher to clear a signal into an occupied approach block (appears as flashing red or lunar in the field) as alternate to a talk-by

Maintenance Bits

(see the ActiveText article for instructions on how to implement these bits on a layout)

  • LC - LocalControl - Plant is controlled from the signal bungalow, not the dispatcher
  • MC - MaintainerCall - Control to light indicator on local control panel or sound horn outside of bungalow, perhaps to ask maintainer to line a route while in LocalControl
  • EC - EmployeeCall - See "MaintainerCall"
  • M0 - ManualOperate (M-ZERO in ATCSmon, not the letter "O", see OrOccupancy) - maintainer sets indication M0K at the bungalow to request the dispatcher to allow local control, which he does by sending a M0Z

Informational Mnemonics

(see the ActiveText article for instructions on how to implement these bits on a layout)

  • AC - AcknowledgementBit - [noted on several control points on CSX Baltimore Division - GP]
  • CU - CodeUnit
  • DA - DoorAjar (the door on the signal house/hut)
  • EQ - EarthQuake
  • GFD - GroundFault
  • HBD - HotBoxDetector
  • HCAL - HighCarloadAlarm
  • HCD - HighCarDetector
  • HCDAL - HighCarDetectorAlarm
  • L0 - LampOut (Note it's L-ZERO in ATCSmon, not the letter "O", see OrOccupancy) Can also mean Local Control (see LC and M0 above)
  • B0 - Bulb Out (same as Lamp Out)
  • P0 - PowerOutage (Same as above, P-ZERO in ATCSmon, not the letter "O", see OrOccupancy)
  • SM - SnowMelter or switch heater/blower, etc. (could also mean Signal MaintainerCall)
  • TE - TimeElement - Plant is "running time" before a signal can be reset
  • TTGZ - ThroughTrainSignalRequestIndication
  • PL - PlantLock - Same as TE
  • SD - RockSlideDetector
  • M - MaintenanceIndication (directional - EM,WM,NM,WM) indicates electrocode malfunction
  • SM - Snow Melter (switch heater)
  • SMF - Snow Melter oFf
  • LA20 - Low Air pressure 20 PSI
  • LA45 - Low Air pressure 45 PSI

Other Mnemonics

  • ERS - EngineReturnCircuit - think this is similar to C0 (CallOn) intending for engines to back across the plant back onto their train? (edit: Yes; this mnemonic is in use on CSX's Boston Sub at certain CPs located adjacent to station platforms. -DWHonan)
  • F - FleetMnemonic (?)
  • FL - FleetMnemonic - tells plant to keep lining up the same route, since there's a fleet of trains due to pass along the same route

Unknown Mnemonics

NOTE These mnemonics were taken from the various tutorials around Yahoo Groups, however, no definition was provided. If you know what any of these are, please clue us in. :)

  • BC
  • BO - Bulb Out (a signal bulb is burned out)
  • DT
  • EC - Employee Call (like Maintainer Call)
  • ENT
  • ENT-N
  • FSK-N
  • HPO
  • NFK-N
  • NSF
  • OSF
  • PO-N
  • SE
  • SFD - possibly SlideFence ?
  • SF-N - possibly SlideFence ?
  • SF-S - possibly SlideFence ?
  • SSF - possibly SlideFence ?
  • TB - Track blocking device
  • TM

-- BrianSwan - 24 Oct 2006