Ameentrainguy, I agree with Don's reply to you, but I'm not sure he was clear about one thing: You can write your software to send exclusively TMCC commands out the serial port, and if you upgrade to Legacy hardware and optionally also Legacy locos -- your software will still work fine. All of the Legacy hardware and all Legacy locos will respond to TMCC commands -- whether from a Lionel TMCC control system or from serial data being spit out of an Arduino serial port. As Don pointed out, the hardware interface will need to be upgraded for Legacy (to include an SER2), but your software will continue to work exactly as before.
My exclusively-Legacy project would work just fine if all I used were TMCC commands -- and my software would be simpler because the TMCC protocol is simpler. The incentive to go with the Legacy protocol is that Legacy equipment offers more control -- more speeds, more control over triggering announcements, controlling smoke, etc. If you look at the plain-English description of the commands in the TMCC protocol versus the Legacy protocol, you'll see what the differences are.
