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Receivers

The Receiver tab page covers set-up. This page is the reference: protocol names for the CLI, Spektrum binding, RSSI and signal-loss settings.

Serial receiver protocols

Set with serialrx_provider, on a UART with the Serial RX function.

serialrx_provider Protocol Telemetry on the same wire
CRSF TBS Crossfire, ExpressLRS Yes
SBUS Futaba S.BUS (inverted) --
SBUS2 Futaba S.BUS2 Yes
FPORT / FPORT2 FrSky F.Port / F.Port 2 Yes
FBUS FrSky F.Bus Yes
SPEK1024 / SPEK2048 Spektrum DSM2 / DSMX satellites --
SRXL Spektrum SRXL (and Multiplex) Yes
SRXL2 Spektrum SRXL2 Yes
GHST ImmersionRC Ghost Yes
SUMD / SUMH Graupner HoTT --
IBUS FlySky iBUS --
IBUS2 FlySky iBUS2 Yes
JETIEXBUS Jeti EX Bus Yes
XB-A / XB-B / XB-B-RJ01 JR XBUS Mode A / Mode B / RJ01 --

The signal options are serialrx_inverted, serialrx_halfduplex and serialrx_pinswap -- see Serial Ports.

Some protocol options:

Setting
sbus_baud_fast Fast (200 kbaud) SBUS, for receivers that support it.
srxl2_unit_id SRXL2 unit ID; 0 for full-size Spektrum receivers such as the AR6610T.
srxl2_baud_fast Fast SRXL2 baud rate.
crsf_use_negotiated_baud Let CRSF/ELRS negotiate a higher baud rate.
crsf_telemetry_mode NATIVE or CUSTOM -- see ELRS Custom Telemetry.
crsf_telemetry_link_rate / crsf_telemetry_link_ratio ELRS packet rate and telemetry ratio, for custom telemetry.

Spektrum binding

SRXL2 receivers bind from the Configurator: Bind Receiver on the Receiver tab, or bind_rx in the CLI.

Satellites bind through the flight controller, which sends the bind pulses at power-up:

  1. Set spektrum_sat_bind to the code for your satellite and save:

    Value Mode
    3 DSM2 1024-bit, 22 ms
    5 DSM2 2048-bit, 11 ms
    7 DSMX 1024-bit, 22 ms
    8 DSMX 2048-bit, 22 ms
    9 DSMX 2048-bit, 11 ms

  2. Power cycle the flight controller. The satellite blinks, ready to bind; bind it from the transmitter.

  3. With spektrum_sat_bind_autoreset = ON (the default) the setting resets to 0 after binding.

The satellite must be powered from a pin the flight controller can switch at power-up (the board's DSM port does this).

RSSI

Source Set up with
From the receiver protocol Automatic for CRSF, F.Port, F.Bus, SRXL2, Ghost and others -- choose AUTO on the Receiver tab.
From a channel rssi_channel -- a receiver channel that carries RSSI.
From an analogue input The RSSI_ADC feature and the board's RSSI pad.
From frame errors rssi_src_frame_errors = ON -- estimated from SBUS frame loss.

rssi_scale, rssi_offset and rssi_invert adjust a channel or ADC reading to 0-100%.

Signal loss

A channel value outside rx_pulse_min .. rx_pulse_max (default 885 - 2115 µs) counts as invalid. What happens then is set on the Failsafe tab; the per-channel fallback values are the rxfail command:

rxfail <channel> <a|h|s> [value]

a = auto (centre, throttle low), h = hold the last value, s = set the given value in µs.