You wired a new receiver to UART 3, selected “Serial RX” in Betaflight, and nothing works. The flight controller sees nothing, your radio won’t arm, and you’re 90 minutes into Googling pinouts. Receiver protocol confusion is the single most common roadblock for new builders. Here’s the wiring and configuration for every protocol you’ll encounter in 2026.
Step-by-Step Serial RX Configuration
1. Identify Your Protocol Before You Solder
The protocol determines which wire goes where. Get this wrong and you’ll spend hours on a non-functional build:
- SBUS (FrSky, Futaba): Inverted serial signal. Connect the RX’s SBUS pin to a dedicated SBUS pad or any UART RX pad with an inverter. Most modern F4/F7 flight controllers have a dedicated SBUS pad with a built-in inverter. If your FC doesn’t, wire to UART RX and enable
set serialrx_inverted = ONin CLI. - CRSF (Crossfire, ExpressLRS): Uninverted serial signal. Connect RX’s TX to flight controller’s RX on any open UART. Connect RX’s RX to flight controller’s TX on the same UART for telemetry. This is the simplest wiring — two wires, one UART.
- F.Port (FrSky ACCESS/ARCHER): Combined SBUS + SmartPort on a single wire. Connect the RX’s S.Port/F.Port pin to any UART TX pad. The protocol runs bidirectional on one wire. In Betaflight, set the Serial RX provider to FPORT on that UART.
- IBUS (FlySky): Uninverted serial signal. Connect RX’s IBUS/SERVO pin to any UART RX pad. Single wire, receive-only. No telemetry on the same wire — you need a separate SENS pin for voltage telemetry back to the radio.
2. Wire It Correctly — Pin by Pin
SBUS wiring (FrSky R-XSR example):
– RX SBUS_OUT → FC SBUS pad or UART RX (with inverter)
– RX S.Port → FC UART TX (separate UART for telemetry)
– RX GND → FC GND
– RX 5V → FC 5V
CRSF wiring (ExpressLRS / TBS Crossfire example):
– RX TX → FC UART RX
– RX RX → FC UART TX
– RX GND → FC GND
– RX 5V → FC 4.5V or 5V pad
F.Port wiring (FrSky Archer RS example):
– RX S.Port/F.Port → FC UART TX (single wire, bidirectional)
– RX GND → FC GND
– RX 5V → FC 5V
IBUS wiring (FlySky FS-iA6B example):
– RX IBUS/SERVO → FC UART RX
– RX GND → FC GND
– RX 5V → FC 5V
3. Betaflight Configuration per Protocol
SBUS:
– Ports tab: Enable “Serial RX” on the UART connected to SBUS
– Receiver tab: Serial Receiver Provider = SBUS
– CLI: If wired to a non-inverted UART: set serialrx_inverted = ON then save
CRSF:
– Ports tab: Enable “Serial RX” on the UART connected to RX TX→FC RX
– Receiver tab: Serial Receiver Provider = CRSF
– Telemetry works automatically over the same UART — no separate configuration needed
F.Port:
– Ports tab: Enable “Serial RX” on the UART connected to the TX pad
– Receiver tab: Serial Receiver Provider = FPORT
– CLI: set serialrx_halfduplex = ON then save (F.Port is half-duplex on a single wire)
– CLI: set serialrx_inverted = ON (F4 FCs need inversion; F7 and H7 handle it automatically)
IBUS:
– Ports tab: Enable “Serial RX” on the UART connected to IBUS
– Receiver tab: Serial Receiver Provider = IBUS
– No special CLI commands needed
Serial RX Protocol Comparison
| Protocol | Wires Needed | Latency | Telemetry | Max Range | Inverted Signal | Best For |
|---|---|---|---|---|---|---|
| CRSF (ELRS 3.x) | 2 (TX+RX) | 4-8ms | Full CRSF telemetry | 30km+ | No (UART native) | Long-range, racers, everyone in 2026 |
| SBUS (FrSky D16) | 1 (signal only) | 14-20ms | Separate S.Port wire | 2-5km | Yes (needs inverter on F4) | Legacy builds, budget whoops |
| F.Port (FrSky ACCESS) | 1 (bidirectional) | 8-12ms | Combined on wire | 3-8km | Yes on F4, no on F7 | FrSky ecosystem users |
| IBUS (FlySky) | 1 (signal only) | 12-16ms | Separate SENS pin | 1-3km | No | Budget builds, trainer quads |
Serial RX Configuration Mistakes
Mistake 1: Sending an Inverted Protocol to an Already-Inverted Input
Some flight controllers have a hardware inverter on the SBUS pad. If you’re wiring CRSF (uninverted) to an SBUS pad (inverted), the double inversion cancels out — but only on some FCs. Worse, it sometimes works intermittently, producing random failsafes that are impossible to debug. Wire CRSF to a standard UART RX pad, never to a labeled SBUS pad.
Mistake 2: Forgetting Half-Duplex for F.Port
F.Port sends and receives on a single wire. Without set serialrx_halfduplex = ON, the FC waits for data on the RX pin but never transmits telemetry back on the TX pin — because the TX pin isn’t even connected. The receiver works (you get stick inputs) but telemetry is dead. This one CLI command is the most common F.Port troubleshooting fix.
Mistake 3: Connecting CRSF RX to 5V Without Checking Specs
Some ExpressLRS receivers (Happymodel EP1, EP2) are rated for 5V maximum. Others (Radiomaster RP1, RP3) tolerate up to 8.4V. If your FC’s 5V rail actually outputs 5.3V under no load, a 5.0V-max receiver will brownout intermittently at range when the onboard LDO can’t regulate. Always check your specific receiver’s voltage range — the ExpressLRS binding guide documents voltage specs for every popular receiver.
Mistake 4: Picking SBUS in 2026 for a New Build
SBUS has 14-20ms latency, a 16-channel limit with only 8 channels above 10-bit resolution, no native telemetry, and requires signal inversion gymnastics. ExpressLRS with CRSF protocol costs the same, offers 4-8ms latency, full telemetry, and is the de facto standard. Unless you’re reviving a 2019 build with an FrSky XJT module, there is no reason to use SBUS in 2026.
⚠️ Regulatory Notice: All radio control systems described in this article must be operated in accordance with the latest 2026 drone regulations in your country or region. ExpressLRS and Crossfire operate on the 868MHz (EU) or 915MHz (US/FCC) ISM bands — ensure your hardware’s frequency band matches your regional allocation. Transmitter power limits vary by jurisdiction. Always verify compliance with your local aviation authority before flying.
Once your RX is bound and talking, dial in your OSD telemetry displays — our Betaflight RSSI setup guide covers LQ and RSSI dBm configuration. For advanced radio setup beyond the receiver, the Betaflight CLI power user guide documents serial diagnostics commands.
The Radiomaster RP1 ExpressLRS receiver is my default recommendation for any 5-inch build in 2026. True diversity with dual antennas, 500mW telemetry output, and the smallest footprint in its class at 11x16mm. Available at uavmodel.com pre-flashed with ExpressLRS 3.5 and your choice of bind phrase.