CPPM period on FrSky receivers

Hello guys,

I am going to buy FrSky D4R-II and a Taranis.

Receiver D4R-II can output CPPM as needed by NAVIO+ as detailed here:


As you can read there is a limitation. CPPM period time is 18mS and the consequence is that you cannot use channel 7-8 (they overlap with 1 and 2 if I correctly understood)

So FrSky offer a firmware upgrade in order to increase CPPM period time to 27 ms:


So you can use all 8 channels.

The question: is there any warning/raccomandation/keep in mind/awareness that I should know in using the installed D4R-II 18ms firmware or the 27ms firmware along with NAVIO+?

Can you briefly comment the limitation described by FrSky with original 18ms firmware with the combined usage with NAVIO+?

Thanks in advance.

PS: the above limitation seems to affect also D8R-XP recevier.

You are probably ok using the original firmware, because the problem only occurs if you use 8 channels and give maximum (2000us or more) input for all channels. Then the gap between the ppm frames gets to short to be detected.
But flashing the alternative firmware is easy. You do not have to use all the cables you can buy from FrSky. A 5V FTDI Basic adapter is enough and you can use it for many other things.
The problem with FrSky is, they use RS232 inverted signaling for all their gear and most microcontrollers use 3.3V or 5V UART. You have to set up the FTDI adapter to use inverted signaling and you are good to go.

Here is the link to a HowTo on diydrones:


There was a discussion on this issue here. Navio uses APM PPM decoding code, so as long as you do as @schuermannsebastian suggested, you are good to go! Update firmware, or don’t use 8 channels.

Now it is definitely clear, thanks for the hints fellows.

The receiver arrived and now it works correctly with navio!