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CC1020 Preamble and Sync Word

Rahul Kulkarni
Prodigy 140 points
Other Parts Discussed in Thread: CC1020, CC1100

I am using the CC1020 ICs in an AX.25 protocol based environment. My problem is that only one byte i.e. 0x7E is recognised as sync word in AX.25, whreas including 2 bytes preamble and 2  bytes Sync word a total of 4 bytes are required for CC1020. How can i configure it to use only 0x7E instead of these 4 bytes as Sync word?

  

  • 0
    TI__Mastermind 39860 points

    The CC1020 does not include any on-chip packet handling such as automatic preamble insertion/detection or sync word insertion/detection. This is all user defined and both insertion and detection needs to be handled by the interfacing MCU.

    We recommend a minimum 3 byte preamble for AGC settling, bit synchronization and for setting the data slicer level correctly. The sync word is used for byte sync and is up to the user to define the number of bytes. We recommend a longer than 1 byte preamble to reduce the likelihood of false sync word detection (i.e reduce the time in Rx processing false packets), but there is nothing inside CC1020 preventing you from using 1 byte sync word.  

  • 0 in reply to Sverre
    Prodigy 140 points

    I have been using the CC1100 chips for a while and they have on chip packetizer which includes automatic preamble and sync word insertion. Is this feature not applicable to CC1020 as mentioned in Section 12.10 of the datasheet?

  • 0 in reply to Rahul Kulkarni
    TI__Mastermind 39860 points

    There is no mention in the CC1020 data sheet regarding automatic on-chip packet handling features. This is something we added for the next generaton devices, which inlcudes CC1100. 

    Section 12.10 in CC1020 data sheet merely explains what is a good sync word and that we have used 3 bytes preamble and 2 bytes sync word when we tested CC1020 sensitivity.

  • 0 in reply to Sverre
    Prodigy 140 points

    Thanks a lot. Your expert advice greatly simplified things.