FrSky ACCST D16 v2 important firmware update

FrSky announced the release of an update to the FrSky ACCST D16 radio protocol. The upgrade is recommended to all users.

The new version has been marked with 2.0.0 (the last update has version 2.0.1) and in this article it will be called ACCST D16 v2 or simply D16 v2. To distinguish the protocol used so far, we will call ACCST D16 v1 or D16 v1.

The original FrSky message can be found here: Important Firmware Update – ACCST D16 2.X.X

In this article we present the Polish translation of the original FrSky message, along with our commentary. The comment is presented based on additional information that we obtained from FrSky from other sources and as a result of our own analysis.

This article will be updated regularly, as long as new information is available.

last updated: 2020-01-21

Why was ACCST D16 v2 released?

The purpose of the upgrade is to increase the reliability and performance of the ACCST D16 (2.4GHz) protocol in difficult wireless environment. In such very specific conditions, with strong radio interference, the D16 v1 protocol may have lost one to few control frames.

The problem occurs extremely rarely, in specific conditions. If it occurs, it can be manifested by an almost imperceptible, very momentary vibration of one or two servos – this is a more frequent case of symptoms. Less often it can cause a temporary but already noticeable “freeze” of the current servo position (RC channels) and / or a change in the position of one random servo (RC channel), not necessarily even used in the model (therefore only temporary “freeze” of the channel position may be visible as a symptom ).

Symptoms occur in both geographical ACCST D16 variations, so both FCC and EU-LBT. However – due to the specificity of LBT – when the problem manifests itself it is much more visible in the EU-LBT firmware (it may be similar to the momentary activation of the failsafe mechanism in HOLD mode, so maintaining the last channel positions). For FCC firmware, the symptom is practically not noticeable (only slight vibrations or even only audible vibrations, which do not translate into any servo movements).

Symptoms appeared so extremely rarely, so that for many years this problem remained virtually unnoticed and had no impact on the vast majority of users. Due to such a rare manifestation of the problem, its diagnostics was extremely difficult, nevertheless the cause was finally isolated and FrSky prepared a firmware update – ACCST D16 v2.

A detailed report on the diagnosis and development of the patch by a test team from Germany, Austria, Switzerland and FrSky is available under the following link:

What was changed?

FrSky has improved error correction to increase data transmission reliability, even under extremely strong radio interference.

At the same time, the data transmission error correction has been increased and most likely an additional security has been introduced in the form of transmission encryption – similar as it is used in the latest FrSky ACCESS radio protocol (the ACCESS protocol is used in the 2019 model series of FrSky transmitters).

Which products ACCST D16 v2 upgrade applies to?

The upgrade applies to all transmitting modules and FrSky receivers currently operating in ACCST D16 v1 (2.4GHz) mode, including internal transmission modules in Taranis and Horus radios.

To date FrSky has released the D16 v2 firmware for the following products.

XJT & IXJT transmitter modules

  • XJT transmitter module
  • Taranis X7 / X7S / X9D / X9D+ / X9D+ SE / X9E / X-Lite radios
  • Horus X10 / X10S / X12S radios


  • XM / XM+
  • X4R / X4RSB / X6R / X8R
  • R-XSR / RX4R / RX6R / RX8R / RX8R PRO
  • G-RX6 / G-RX8
  • S6R / S8R

Embedded receivers


Few receivers and transmitting modules are still missing on the above lists, e.g. XMR, XSR-M, XJT Lite, etc.

Soon FrSky will also publish updates for ACCESS transmitting modules (ISRM series transmitter modules built into i.e. Horus X10 / S Express, X-Lite S / Pro), which can also work in D16 mode. In this case, however, the update will only be relevant if ACCST D16 is actively used. If the ISRM transmitter module is used in ACCESS mode only, it is not necessary to update it due to the ACCST D16 v2 upgrade.

However, the ACCST D16 v2 firmware upgrade for ACCESS tranmitter modules is not available yet . Therefore, upgrading D16 receivers to version D16 v2 will make them impossible to use with ACCESS transmitters (e.g. Horus X10 / S Express, X-Lite S / Pro). In this case, you must wait until the ACCESS D16 v2 firmware for ACCESS transmitters will be available for download on the FrSky website.

Which products are not affected?

The upgrade does not apply to transmitter modules or receivers operating in D8 and LR12 modes. These are all transmitter modules and receivers of the V series, D series and LR – i.e. V8FR-II, D4R-II, D8R-II Plus, L9R receivers; DJT, DHT, DFT transmitter modules.

The update also does not apply to receivers operating in the ACCESS protocol nor to any products of R9 series.

Some receivers – e.g. RX4R, R-XSR, etc. – can work with ACCST or ACCESS firmware, at user’s discretion. If they work with the ACCESS firmware, the upgrade does not apply to them. However, if they work with ACCST firmware – the firmware should be updated to the latest available ACCST D16 v2 version.

As new information becomes available, we will update the above lists on an ongoing basis.


FrSky recommends updating all your ACCST D16 receivers and transmitter modules.

Impact of upgrading / Compatibility

Due to the improved validation of ACCST D16 v2 data transmission, and introduced additional security (encryption), the ACCST D16 v1 and v2 protocols are not compatible with each other. Therefore, the upgrade to ACCST D16 v2 should be carried out for all D16 receivers and transmitter modules, also build-in modules of Taranis and Horus radios (see the above lists).

Most likely newly distributed D16 receivers will be delivered with ACCST D16 v2 firmware only. This will also apply to the D16 mode on ACCESS transmitting modules.

ACCST D16 v2 does not change anything about FCC and EU-LBT compatibility. As before the firmware of the transmitter modules and receivers will have to be aligned, that means that FCC or EU-LBT should be used in all your transmitting modules and receivers (EU-LBT firmware should be used in Europe).

How to upgrade firmware?

Firmware upgrade is a simple operation that is recommended to do as a normal maintenance regardless of the ACCST D16 v2 release.

Updating the firmware of FrSky receivers and transmitter modules (more generally FrSky Smart Port devices) is possible using a computer and a special programmer, or using any FrSky radio (with FrOS or OpenTX 2.1 or newer).

We have prepared the following articles to help with the upgrade:

The above articles are published in Polish only. Please use some on-line translator or search for other, English resources covering these topics.

Stay tuned

The announcement about the ACCST D16 v2 upgrade appeared just recently (January 16, 2020), and the original FrSky message was quite laconic. We will make every effort to ensure that this article is a reliable and up to date source of information about the change introduced by ACCST D16 v2.

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