What Legacy features are not available on TMCC?

I  ordered a base 3 and have had similar thoughts as I wait for my base 3 to show up.

Here is a good thread with a lot of information: https://ogrforum.com/...ween-tmcc-and-legacy

There are also a bunch of you tube videos like this one:

Smoking  whistle on a Lionel even works in conventional- so yes, that feature works under TMCC.

List your engine product number, but more importantly read the manual specific to that engine- it actually answers this question in more detail than we can guess to provide here. I'm saying that because we could go down some crazy rabbit hole of all known legacy commands, or just the ones your engine supports. The engine manual has distinct section for TMCC command, and then another for Legacy. I don't know of any manual with a chart that says these features compared to Legacy don't work under TMCC.

Part2- TMCC VS Legacy is mostly limited by the base you choose, and the cabling system you use to connect DCS to to base, and then also, what features in Legacy that engine has that requires unique commands. Again, the real limitation- an old TMCC base can only ever send TMCC flavor commands, but even a Legacy base, they want the SER2, the MTH TIU to Lionel cable, for "full maximum Legacy" compatibility. So even then, I would think there are some engines that might have specialized Legacy commands that the MTH system is not able to send.

Dual colored class/marker lamps, specialized aux3 commands? Come to mind that I wonder if they can be commanded from a DCS remote or app.

Re: "What other features are not accessible?"

A look into the LCS-Legacy Protocol Specification (referenced HERE) provides insight into the additional commands that Legacy locomotives can receive.  In brief, the protocol specification describes the original TMCC1 commands, the Legacy TMCC2 commands, and the Legacy extended commands.

The TMCC1 Engine and Train commands are limited to 32 speed steps, Train and Route IDs are 1 through 9.

TMCC2 replaces Engine and Train commands with 200 speed steps, Train and Route IDs are 1 through 99.  Quilling whistle/horn plus dialog and effect trigger are added.

Legacy extended commands,  currently defined in the specification, are:

    Dialog control of additional dialogs (i.e. fuel level, current speed, emergency stop, conductor "all aboard", and many more),
    Sequence control (i.e. press and hold the AUX1 button for three seconds for scripted CrewTalk and TowerTalk dialogs),
    Station Sounds Car dialog controls,
    Effects control (i.e. master and prime mover volume, cylinder cocks, couplers, subway doors, pantographs),
    NYC Subway Car Station Stop dialogs,
    Sound masking (play always, play never),
    Lighting control (i.e. Rule 17, Cab, Mars, Strobe, Ditch, Hazard, Ground, Doghouse lights on/off/auto).

The extended command sets do not apply to all engines.  You may have to buy a Vision Line engine to enjoy many of the extended command features.

Back to the OP's question ...

The original  Cab1 and base use the TMCC1 commands which have limited addresses and 32 speed steps.

The Legacy Cab2 and Base support expanded addresses and 200 speed steps, quilling whistle, and can control all of the commands (TMCC1, TMCC2, and extended) based on the engine's profile (and supported by the Cab2 and base software updates).

If you have a Cab1L, it depends.  Some Legacy command/features are accessible from the handheld.   The entirety of the Legacy protocol (TMCC1, TMCC2, and extended) may be supported(*) by the Cab1L base, but without a user interface (handheld or app) to trigger Legacy features, you are limited to a subset of Legacy features.

(*) I don't have a Cab1L so I can't verify this.

Re: Whistle steam.  On a non-Vision Line loco, a log of captured commands transmitted by a Base2 shows that triggering the whistle (and steam) used TMCC2 whistle commands.  The logic to issue whistle steam resides in the loco (and there is a on/off switch for whistle smoke).  However, the smoke level was set using Legacy extended commands.  The loco is backwards compatible for TMCC1 commands so setting the smoke level using the AUX1+8 and AUX1+9 buttons should also work.

Re: MTH DCS remote compatibility.  Software updates define how the DCS system issues commands to a Lionel base.  The TMCC1 command set is supported.  The extent of DCS utilization of the TMCC2 and Legacy extended commands is unknown.

@Vernon Barry posted:

Smoking  whistle on a Lionel even works in conventional- so yes, that feature works under TMCC.

List your engine product number, but more importantly read the manual specific to that engine- it actually answers this question in more detail than we can guess to provide here. I'm saying that because we could go down some crazy rabbit hole of all known legacy commands, or just the ones your engine supports. The engine manual has distinct section for TMCC command, and then another for Legacy. I don't know of any manual with a chart that says these features compared to Legacy don't work under TMCC.

Part2- TMCC VS Legacy is mostly limited by the base you choose, and the cabling system you use to connect DCS to to base, and then also, what features in Legacy that engine has that requires unique commands. Again, the real limitation- an old TMCC base can only ever send TMCC flavor commands, but even a Legacy base, they want the SER2, the MTH TIU to Lionel cable, for "full maximum Legacy" compatibility. So even then, I would think there are some engines that might have specialized Legacy commands that the MTH system is not able to send.

Dual colored class/marker lamps, specialized aux3 commands? Come to mind that I wonder if they can be commanded from a DCS remote or app.

I am currently planning a new O scale layout and am interested in the new Lionel Legacy 2-8-0 — 2231090. I do not have any Lionel control systems, only currently have a MTH TIU and WIU for all my MTH things (all of my engines in HO and G are MTH)

So I guess the issue is that the new Lionel base 3 is delayed until end of 2023. If I have my layout running before then I’d like to control the engine obviously. So I’m wondering if I get a TMCC control base to hook up to DCS - what new legacy features do I miss out on?

So far the only ones I see are more speed steps, additional crew talk, quillable whistle. All that are not very important to me

Some of the Legacy features on that locomotive may be activated by using Bluetooth

All the basic running features will be available using TMCC.  Many times I run my Legacy using the CAB1L, it's just a bit more convenient to grab it and it's a good size.