OpenRcBus

OpenRcBus - work in progress

OpenRcBus is an open and expandable protocol to be used between Transmitter - radiomodule or recevier - flightcontroller.

It will interleave RC control and telemetry inside a single serial link.

Physical layer

3v3 TTL level serial port at 1M bauds (tbd.)

Bidirectional link if needed, both directions use same frame types.

High level frame format

[HEADER]
[DATA]
[CRC16]

Header

[PREFIX]   single byte of value '0x??' tbd.
[LENGTH]   length of data part in bytes [0..255], excludes HEADER and CRC16
[DATATYPE] single byte identifying the format of the DATA

Datatype values

0x01 12 bit RC channel data (2 channels per 3 bytes)
0x02 Serial telemetry

Data

Data (0x01)

RC data [FLAGS] - 0x01 -- set failsafe X * ( ch0bits_11_4 | ch0bits_3_0,ch1bits_11_8 | ch1bits_7_0 ) - Channel values (3 bytes per 2 channels)

nominal 1..2ms channel is mapped to values 1024..3071

when setting failsafe special values are used for special behavior
0x000 - do not output channel in failsafe
0x3ff - channel outputs last good value on failsafe

Serial telemetry (0x02)

Serial telemetry of one of following formats, first byte gives subtype.

Subtype values:
0x00 - passthru (transparent data)
0x10 - frsky 'D' telemetry
0x11 - frsky 'smaprtport' telemetry
0x18 - HoTT
0x20 - mavlink
...

CRC16

CRC16 value over HEADER and DATA parts. Calculation details tbd.

WIP

mixer sync

Special frame to inform when new RC data is expected, sent out a fixed time interval e.g. 10ms? before new RC data is needed.