nRF905 preamble

RE: nRF905 preamble

Witek — Tue, 18 May 2021 06:27:47 GMT

Hello Inubot,

Been a while.

Thanks for this info. It certainly helped... But I am not getting a reliable communication between the chips. If I am able to receive a message in nRF905 then it sometimes is correct and sometimes is mangled up depending on what I send in the message. For the time being I am not using CRC checking, just to keep it simple.

Can you confirm that you were albe to get the two devices communicate reliably?

Thanks

Witek

RE: nRF905 preamble

Inubot — Wed, 15 Jul 2020 07:06:09 GMT

Hi Witek,

I have used the S2-LP DK GUI (https://www.st.com/en/embedded-software/stsw-s2lp-dk.html) to tinker with the register values of the S2-LP to match the RF parameters of the NRF905.

In my case the S2-LP was setup with the following radio settings (have a look at the above link for a screenshot of the DK):

433 MHz freq base (assuming no channel offset on NRF905)
100 ksps data rate (data transmission rate of the NRF905)
50 kHz freq deviation (typical freq deviation of NRF905)
250 kHz channel filter
Max power ticked

For the packet settings, you need to remove the preamble, sync word, length and CRC segments of the packet structure, and uncheck data whitening. You should only be left with the payload section of the packet.

In order to transmit data from the S2-LP to an NRF905 device, you will have to build up the payload to include the NRF905 preamble and address before the actual transmission data, followed by the CRC:

1111110101[Address][Data][CRC]

This entire stream should be written to the TX buffer of the S2-LP.

If done correctly, the NRF905 should pick up the transmission and an interrupt should be triggered on the DR pin. You can also use the AM pin to help with troubleshooting.

Hope this helps!

Regards

RE: nRF905 preamble

Witek — Wed, 15 Jul 2020 05:49:40 GMT

Hello Inubot,

It has been a while but thanks for sharing your experience.

I am facing the same task as you did. Would you be able to share more info on how you set up the S2-LP chip to enable the two to communicate.

Any info will be appreciated.

Thanks

Witek

RE: nRF905 preamble

Inubot — Fri, 23 Aug 2019 09:43:38 GMT

I also ran into this problem with no answers online. I needed an S2-LP device from STMicroelectronics to communicate with an NRF905 in a legacy system. After a few days of reverse-engineering multiple packets sent by an NRF905 device, I was able to decode the preamble and CRC algorithm:

Preamble: 01010101010110011001 (Manchester IEEE encoded) 1111110101 (bits)
CRC uses the CRC-16/CCITT-FALSE algorithm

The raw bitstream you need to send then becomes 1111110101[Address][Payload][CRC]. Remember that the bitstream that is transmitted should first by Manchester IEEE encoded!

Hope this helps!

RE: nRF905 preamble

El Farissi — Mon, 13 May 2019 13:47:46 GMT

I agree with you! but I am using a receiver different than nRF905 an I want to know the content of the preamble to have an idea of the whole frame send by the nRF. where can I find the content of the preamble?

RE: nRF905 preamble

run_ar — Mon, 13 May 2019 13:09:50 GMT

The preamble is used by the receiver to lock on to the signal. Not something the application mcu need to handle.

RE: nRF905 preamble

El Farissi — Mon, 13 May 2019 09:57:33 GMT

Thank your for your Answer. Do you have any idea about the content of the preamble because I need to handle it by the receiver?

RE: nRF905 preamble

run_ar — Mon, 13 May 2019 08:03:22 GMT

[quote user=""]My question is: it is possible to remove the preamble and the address and keep only the payload? If not, what does 10 bit of the preamble looks like?[/quote]

No. That is not possible.