I'm in the middle of fact gathering for a personal project in which I want to use TMCC to control locomotives in a different way then currently done. This older OGR post has been helpful and I have a copy of the Complete TMCC Guide with the codes in it, but I have a couple of questions I haven't found any answers to yet.
The TMCC guide says that the codes are 16 bits long from the Cab remote to the base. I'm assuming it's also 16 bit from the base to the locomotive. Now internal of the locomotive from the TMCC receiver, does it only output the last 7 on the serial pin to the RailSounds board?
In looking at the graphs from the above linked thread, is the signal read right to left? That's the only way I was able to figure out how to make it match the commands in the TMCC guide.
What is the reading on the serial pin of the TMCC receiver when there is no TMCC signal? In other words, how is the R2LC (or R4LC) telling the rest of the locomotive it's in conventional mode so that it'll use the DC offsets on the rails for the bell and horn/whistle? And when the HALT command is issued, what does the R2LC send out to the rest of the locomotive? And could someone explain the the blow horn 1 and blow horn 2 commands and how you trigger them with one one horn button on the Cab? And how does the AUX1(2) on/off/option 1/option 2 work? Which does the Cab send when you push the AUX button? Which commands in the whole list (Like the engine extended commands.) are received and kept by the R2LC and which get passed on in the serial output?
The uP in the Cruise Commander M and the K-Line cruise handles the finer speed steps, as well as TAS EOB boards. That's why they're only available in relative mode, which allows the R2LC to just send out "go faster" or "go slower", and not really care about the actual speed setting. It's also why the Legacy R100 mode throttle graph is just a guess, as it is frequently way off, especially if you move the throttle quickly.