The display to host messages is stateless and modeless.
'B' - Button Press
Debounced button data, sent on release. The data is abstracted, each button has a binary value mapped to it. This is to enable a subset of buttons to be implemented if all buttons are not available.
| Button | Value | Meaning |
| Enter | 1 | Enter the menu system |
| Right | 2 | Enter submenu, skip forwards, tune up |
| Don't use | 3 | Unused, causes very strange behaviour in the message |
| Left | 4 | Leave submenu, skip backwards, tune down |
| Up | 5 | Move up in menu, volume up |
| Down | 6 | Move down in menu, volume down |
| Radio | 7 | Immediately switch to radio mode |
| Mute | 8 | Immediatly set volume to 0 (full quiet) |
| mp3 | 9 | Immediatly switch to mp3 mode |
The last three entries are examples of unrequired buttons, they where added as the steering wheel controls incorporated them, but all the operations are available through the menu system and other buttons. More buttons will be added with incrementing numbers. The player software and frontpanel firmware will require extending to handle new buttons, but the existing code needn't change. This will allow backwards compatability.