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CC1120: Check the preamble of the RX message

Luca Filippucci
Prodigy 110 points
Part Number: CC1120

Tool/software:

HI, my CC1120 receives messages from many devices, some with preamble 0xAA and others with 0x55
and it seems strange to me because I configured it to handle only 0x55.

My configuration is this:

CC112X_PREAMBLE_CFG1 , 0x11, // preamble 2 bytes (n*01 whit n=8) 0x55
CC112X_PREAMBLE_CFG0 , 0x22, // preamble decision enabled

Why am I getting both 0x55 and 0xAA? I configured the device specifically to filter traffic in RX.

OK. Assuming that in RX I cannot filter, but how can I know the single message with which preamble it was received?

Has anyone ever had a problem like this?

Thanks.

Luca

  • 0
    TI__Guru* 78051 points

    Hi Luca,

    Could it be the threshold value in PQT is too low, thus letting the wrong packets through? 

    Also, for the receiver the 0xAA and 0x55 preables look very similar since they both consist of 0101010 sequences.

    Can you post the configuration for each member of PREAMBLE_CFG1 and PREAMBLE_CFG0? I.e. PREAMBLE_WORD , NUM_PREAMBLE , PQT, PQT_VALID_TIMEOUT, PQT_EN?

    Cheers,

    Marie H

  • 0 in reply to Marie H
    Prodigy 110 points

    Hi Marie,
    the detailed configuration is:

      NUM_PREAMBLE:       2 bytes 
      PREAMBLE_WORD:      0x55 
      PQT_EN:             yes
      PQT_VALID_TIMEOUT:  16 symbols
      PQT:                2

    “Could it be the threshold value in PQT is too low, thus letting the wrong packets through?”
    Do you mean it could be my configuration that makes me pass packets with the preamble that I don't want?


    Thanks

    Luca

  • 0 in reply to Luca Filippucci
    Prodigy 110 points

    Hi Marie,

    do you have some news for me?

    Regards

    Luca

  • 0 in reply to Luca Filippucci
    TI__Guru* 78051 points

    Hi Luca,

    In general, it's hard for the device to distinguish between 0x55 and 0xAA preambles. It might be possible to achieve this by setting a very strict PQT, but you risk loosing packets. 

    I would advice you to use the sync word to separate these packets. You can shorten the preamble and lengthen the sync word to make the 0x55 sequence part of the sync word.

    Cheers,

    Marie