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#SBus client
## Overview
## Protocol
### Technical details
Because it would have been to easy to use standard settings, the SBus serial communications uses:
* A baudrate of 100000 b/s * An inverted logic * One parity bit * Two stop bits
Luckily, the Teensy3 can manage that 
The SBus protocol sends a message every 7ms (high speed mode) or every 14ms (low speed mode).
### SBus protocol
A common SBus message requires 25 bytes of data:
F0 xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx yy 00
* (0x)F0 is the start byte. It should always be 0xF0. You can sync on that I guess if you want to. * (0x)xx are the data bytes. There should be 22 of them
SBus manages 16 analog channels, and uses 11bits for each, so 11*16/8 => 22 bytes. They could have made our lives easier and used 12bits per channel, but No... So: * CH1 uses the first data byte (let's call it D0), and the 3 Most Significant Bits (MSB) of D1 * CH2 uses the 5 Least Significant Bits (LSB) of D1, and the 6 MSB of D2 * And so on... CH3 uses the 2 lSB of D2, the whole D3, and the MSB of D4...See, its not that easy to process...
* (0x)yy is the flag byte
- Bit 7 (0x80) is CH17, it's a digital/binary channel.
- Bit 6 (0x40) is CH18, same.
- Bit 5 (0x20) indicates a Lost Frame
- Bit 4 (0x10) indicates Failsafe mode
- Bits 3-0 are not used and sould be 0
* (0x)00 is the stop byte. It should always be 0x00. You can also do some check to check there was no lost/added byte in the serial communication.
### Typical Frame
F0 2E 90 FB 1F 1D EC 8E 0F B6 F3 DE 07 C6 A0 D4 1A 83 50 6A 0D 41 A8 00 00
* Starts with 0xF0 * Flag is 0x00, no error. * Ends with 0x00
### Radio off
If the receiver was getting data and then looses the connection (eg, if you turn off the transmitter). It outputs something like this:
F0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 30 00
The only interesting byte is the flag byte; 0x30 means the receiver is in failsafe mode and that a frame was lost (no kidding :-°). Good
## Code
## Links
* http://forum.pjrc.com/threads/23956-Teensy-3-UART-settings * http://developer.mbed.org/users/Digixx/notebook/futaba-s-bus-controlled-by-mbed/