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CC1110 FEC and variable length packets

David Vandewalle
Prodigy 30 points
Other Parts Discussed in Thread: CC1200, CC1101

The CC1110 datasheet states that radio FEC is only for use with fixed length packets.  I recently noticed that we had been running DEC in our application for some time in variable length mode.  It seems to work just fine.  I also noticed the older CC1110 datasheets do not have the fixed length restriction in them.

Does anyone here have a history of why the current part is restricted to FEC in fixed length mode only?  I would love to know what the failure mode (I'm assuming there was some errata at some point that drove this?) is. 

  • 0
    TI__Guru* 79271 points

    When using FEC together with variable packet length there are issues related to receive packets with length byte = 1. Even if your protocol never sends packets with length byte 0 1 will there always be a change that you find a “false” sync word and that the next byte after sync found is 0x01.

    One of the things that will happen in this case is that the MCU will get an indication that a sync word is found but it will never get a "packet received" indication.

    BR

    Siri

     

  • 0 in reply to Siri
    Prodigy 90 points

    Does this same limitation to using FEC with variable packet length also apply in the CC1200?  We would like to use the FEC without the 802.15.4g option. The CC120X Users guide does not list a warning about using it with variable length packet option. Also, the Users Guide does not indicate, but we assume, that the FEC covers the two optional length and address fields. 

    Thank you,

    Don

  • 0 in reply to Don Schaefer
    Prodigy 30 points

    hi.

        i was trying to sent a byte of data from a cc1101 tranceiver.i was able to write and read configuration registers.and configured using rf smart studio..I got status correctly when strobe commands for transmission and reception and other strobes too.i hope i successfully write 1 byte to transmit fifo since i monitored the no of byte status it was seen as 1 and after i strobe stx no of bytess become 0 and transmissionfifo underflow  status become 1.But when tried to read rx fifo some random values are read which was changing randomly.can anybody tell why i couldn read it and is it because i was reading empty fifo?How can i solve this issue? 

                                  Kindly anybody help me pls..if you need i will attach the configuration i did.

  • 0 in reply to mohammed shareef
    TI__Guru**** 317180 points

     mohammed Shareef: This thread is related to the FEC on CC1110. As far as I can see your question is about something else. Could you please start a new thread with your question? Have you tried to look at the easylink example here: http://processors.wiki.ti.com/images/b/b5/Cc1101_easy_link_trxEB.zip? Also write which harware you are running one, your own board or EM? Also try to to format your text differently because it's hard to read. 

  • 0 in reply to TER
    Prodigy 90 points

    TER,

    Will you be able to reply to my question on 7/19 regarding variable length packets and FEC?  Would it be better to start another thread?

    Thank you...Don

  • 0 in reply to Don Schaefer
    TI__Guru**** 317180 points

    The person with the best overview of CC1200 and FEC will be back 4. August. If you are able to wait a week and start a new thread then you will have a better chance of getting an answer.