FrSky receiver feature chart

For posterity, some useful details to compare FrSky ACCST receivers. Last updated 26th March 2024.

PLEASE NOTE:

• This table lacks all of the Archer, Twin and Tandem range of ACCESS receivers.
• It also lacks information about which receivers support F.Port (either with additional physical pins or firmware)

If you can help, let me know.

Transmission Modes

There are five transmission modes of FrSky receivers, from oldest to newest:

• ACCST V8 - non-telemetry channel-hopping, upto 8 channels.
• ACCST D (D8) - stands for "duplex" (meaning two-way). The protocol supports telemetry, and upto 8 channels. Note that the "V*-II" generation of receivers can use this protocol, but do not support telemetry.
• ACCST X (D16)- uses a more advanced way of communicating between the radio and the receiver (PXX). Supports upto 16 channels and telemetry.
• ACCST L (LR12) - long range, no telemetry, uses PXX modulation, upto 12 channels.
• R9 - long range over 900 Mhz, no telemetry, uses PXX modulation, upto 12 channels. Only compatible with specific transmitter
• ACCESS - a closed-source encrypted protocol with both 2.4 GHz and 900 MHz variants, upto 24 channels and features such as OTA updates and automatic rebind

Telemetry

The "V8", "L" and "XM" series of receivers do not support telemetry - they lack an RF transmitter to send data back to your radio. The "D" and "X" receivers all support transmission of "received signal strength" (RSSI), but support three different methods of connecting sensors to report other information:

• Analog: Up to 2 analog input ports (A1 and A2) for simple voltage-based sensors. Some receivers have A1 internally connected to measure the receiver's voltage, with A2 open for external sensors (e.g. for flight battery voltage).
• Digital: The digital port on D-series receivers allows connection of more complex sensors such as a variometer. Multiple sensors can be connected via a hub.
• Smart Port (S.Port): This newer mechanism on X-series receivers uses a full-duplex (two way) digital serial communication over a single signal wire. Sensors can be chained together and a hub is not required.

RSSI Out

All models with telemetry will report the Received Signal Strength Indicator (RSSI) to your transmitter. However some receivers can output it through a servo channel, i.e. either a physical PWM output or an SBUS channel (see the manual). This generally means sacrificing a channel or some other function of the receiver, but is particularly useful for FPV pilots. The RSSI signal strength is sent to a flight controller so that it can be embedded alongside other telemetry in an on-screen video overlay that is transmitted back to the pilot's goggles/screen.

Control Outputs

There are two main ways of getting a control signal out of the receiver and to your flight controller, ESC or servos:

1. Receivers designed for use in traditional aircraft without a flight control have PWM servo outputs, each with 3 pins (signal, V+ and V-)
2. Many receivers, both with and without PWM outputs, can also output a digital signal.

There are via a few different protocols for digital outputs (intended for flight controllers, stabilisation systems etc):

• The V8 and D generation receivers both use PPM modulation, which can carry upto 8 channels. Some receivers can output a combined CPPM signal on a 3-pin connector (either dedicated or one of the servo outputs), which is basically a sequential ordering of the raw PPM data.
• The X generation receivers can use PXX, which has upto 16 channels, lower latency and features such as ModelMatch. Most of these receivers can output combined channels via the Futaba SBUS protocol, normally via a dedicated output. A few are switchable to CPPM too.
• Later ARCHER receivers support F.Port, which functionally replaces both S.Port and SBUS for both telemetry and controls on a single wire.

A note regarding SBUS: it can be a source of great confusion that receivers and flight controllers describe "inverted" SBUS signals, with some hardware and software offering a way to switch between them. This phenomenon originates because the original Futaba implementation is based on the RS232 (UART) protocol but with some changes, one of which was to invert the signal (i.e. positive voltage is 0 and ground is 1). Since a lot of microcontrollers used for flight controllers and receivers have hardware UART implementations, using one of these for SBUS means the signal will be inverted compared to SBUS, albeit 'right way round' for UART. Hence it's necessary to implement additional pre/post-processing software/hardware.

A note regarding F.Port: Unfortunately I have not had the time to update the table with which receivers support F.Port. Later receivers have dedicated F.Port pins in addition to S.Port and SBUS pins; others like the R-XSR have firmware updates available, but it also updates to ACCST v2, for which transmitters must also be updated. Unfortunately the two are incompatible - updating the transmitter breaks compatibility with any older ACCST receivers.

Redundancy

The 'R' range of X series receivers (R-XSR, RX6R, RX8R, RX8R PRO, G-RX6, G-RX8, R9, R9 slim) feature a redundancy option.

High Speed servos

Some D-series and X-series receivers have an option for a faster update rate from their PWM servo ports. This is 9ms, compared to the default 18ms.

Stabilisation

The S6R and S8R receivers add a 3-axis stabilisation feature to the X6R and X8R respectively.

Variometer

The G-RX* range are designed for gliders and have an integrated variometer.

FASST receivers

I haven't collated the features for the TF range of FASST receivers but may do in future. Feel free to send me a list of the stats and I'd be happy to add them.