nRF905 preamble

[El Farissi]

Hi everyone,

I am working on a project using nRF905 as an emitter and another Receiver(different than nRF905), the receiver is programmed in a way to perform some actions only when it received a specific frame(for example: 0x156666) but after reading the data sheet I found that in each data packet transmitted by the nRF905 a preamble is added automatically in addition to the TX address.

As a result, the frame at the output will be: [preamble][Address][0x156666][CRC]

I found that CRC can be disabled so the data frame will be :  [preamble][Address][0x156666]

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?

I will be very grateful if anyone could help me to fix this problem.

Best regards

[run_ar]

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?

 No. That is not possible.

[El Farissi]

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?

[run_ar]

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

[El Farissi]

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?

[Inubot]

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!