There are four transmission modes of FrSky ACCST receivers, from oldest to newest:
- V8 - non-telemetry channel-hopping, upto 8 channels.
- D - 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.
- X - uses a more advanced way of communicating between the radio and the receiver (PXX). Supports upto 16 channels and telemetry.
- L - long range, no telemetry, uses PXX modulation, upto 12 channels.
The "V8" and "L" series of receivers do not support telemetry. The "D" and "X" receivers all support transmission of "received signal strength" (RSSI), but support three different methods of connecting sensors:
- 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: 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.
- 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 useful for example for multicopter control boards.
- The X generation receivers can use PXX, which has upto 16 channels, lower latency and features such as ModelMatch. These receivers can output combined channels via a separate Futaba S.Bus port.
High Speed servos
Some D-series receivers have an option for a faster update rate from their PWM servo ports. This is 9ms, compared to the default 18ms.
|Receiver||PWM Servo outputs||Pins||Range||Protocol||
|Combined output||RSSI out||Analog 1 input||Analog 2 input||Digital telemetry input||High Speed Servos|
|D4R-II||4||end||1.5km||D8||yes||yes||CPPM (8)||yes||internal voltage||yes||Hub Protocol||no|
|D8R-XP||8||end||1.5km||D8||yes||yes||CPPM (8)||yes||yes||yes||Hub Protocol||yes|
|D8R-II Plus||8||end||1.5km||D8||yes||yes||no||no||yes||yes||Hub Protocol||yes|
|X6R||6||end||1.5km||D8/D16||yes||yes||S.Bus (16)||no||internal voltage||yes||Smart Port||no|
|X8R||8||end||1.5km||D8/D16||yes||yes||S.Bus (16)||yes||internal voltage||no||Smart Port||no|