I typed this from memory, hope I got it right .. . :-)
Futaba S.Bus for Paparazzi Date: Thu, 25 Aug 2011 09:46:07
Hi Eric and Martin
The Futaba S-BUS protocol. Timing In normal mode, the receiver every 14 ms, a frame is sent in the high-speed mode, all 7ms. A frame (25 bytes) lasts 3ms.
Data Format The baud rate is 100.000Bit / s (not compatible with 115.200Bit / s) - look for in a development that is on the appropriate processor Quartz and prescaler
The format is 8E2 (1 start bit, 8 data bits, 1 even parity bit and 2 stop bits) The bits are transmitted inverted (0V = High)
The data The first byte is always 11110000 The next 22 bytes contain 16 servo position without channel number A record consists of 11 bits per channel, LSB first (least significant bit first), range 0-2047, 1024, the center The data here jump on the byte boundaries, ie: Channel 1 requires the second Byte of the sequence to the first 3 bits of the third Byte. Channel 2 uses the remaining 5 bits of the 3rd Bytes, plus the first 6 bits of the fourth Byte.
The last byte contains 4 flags (and 4 with unknown importance): Flag1: DG1 (channel 17, digital switching channel 1) Flag2: DG2 (channel 18, digital switching channel 2) Flag3: Lost frame Flag4: failsafe indicator Flag5:? Flag6:? Flag7:? Flag8:?
In conclusion, there's still a 00000000 There is no checksum, error correction codes or encryption.
Evaluation The analysis is extremely simple. All servos must be programmed. Here they are assigned a channel, i.e. is a data packet, it will be read and considered the position of the servo data from the saturated part of the rich data packet out.
Conclusion As you can see, the S-BUS is a very simple structured serial data transmission without checking whether the data was correctly transferred. Apparently here is placed on the repetition of the data, but can vary in nature and response components already connected the wrong lead or disturbed by external factors in the model frame to unwanted events.
Buy Cheap, Buy Twice . . .