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CC110L: receive issue when receving continuous 0xFF followed by non 0xFF bytes from AMICCOM A7139

Jianyi Bao
Expert 2220 points
Part Number: CC110L
Other Parts Discussed in Thread: CC1200

Hi, Experts:
We have a CC110L board that needs to receiver data from AMICCOM A7139 (http://www.amiccom.com.tw/). Some settings are:

433M, 250kbps, GFSK, Fdev=127 in CC110L and 93k in 7139.

A strange thing is that: If the transmitted data from 7139 contains a lot of continuous 0xFF, the bytes following the final 0xFF will probably fail in Rx side (CC110L).

However, another 7139 (as Rx) could receive it correctly. I believe CC110L to CC110L communication has also no problem with continuous 0xFF.

I didn't test if continuous 0x00 will make the same result. If the data is random, the result will be OK.

See the picture (Sending many FF followed by 3E B9). The last 3 bytes in CC110L Rx side becomes FE 7D 73. And it could be found that exactly one bit is shifted from "FF 3E B9" to "FE 7D 73"

It looks that Bit sync in CC110L may fail in this condition as the bits are all 1. But I wonder why CC110L to CC110L has no problem.

Enabling data rate offset compensation by setting BSCFG.BS_LIMIT[1:0] to non-zero could increase the success rate, but still there is error sometimes.

Any idea about the cause?

  • 0
    TI__Guru**** 317180 points
    For payloads that contains a lot of equal '0x00' and '0xFF' we normally recommend using whitening or other methods to ensure that you get bit transitions. If the payload doesn't contain transitions the tracker risk loosing the decision limits for what a '1' and '0' is.

    Is the packet you are testing with a realistic one?
  • 0 in reply to TER
    Expert 2220 points

    Our real packet could contain coutinuous FF or 00.

    Could manchester coding solve this issue, since there is always a level transition for each bit? Does manchester coding decrease sensitivity, because the data rate on the air is doubled?

  • 0 in reply to Jianyi Bao
    TI__Guru**** 317180 points
    Manchester will degrade sensitivity since you are doubling the the datarate and the air and hence you need to increase the Rx Bw but it will most likely solve the issue. Are you able to use whitening?

    On a side note: CC1200 should be able to receive these long 0xFF sequences since it's possible to adjust how fast the adjustment loops are.
  • 0 in reply to TER
    Expert 2220 points
    I can use whitening. Thank you.