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CC1101: CC1101 synch word detection issue

frederic simon82
Prodigy 20 points
Part Number: CC1101
Other Parts Discussed in Thread: TEST2

hello

i am using a CC1101 to  transmit this kind of frame : {0x55,0x55,0x55,0x55,0x55,0x55,0x55,0x55,0x55,0x55,0x00,0x00,0x00,0x00,0x1F,0xFF,0xFF,0xFF,0xFB,0x23,....,}

i use another CC1101 to receive it . when i configure (SYNC1,SYNC0) = (0x55,0x00) or (0x55,0x50) or (0x50,0x00)  the CC1101 succeed to find it and receive the frame

but when it configure i configure (SYNC1,SYNC0) = (0x00,0x00) or (0xFF,0xFF) or (0x00,0xFF) or (0xFF,0xFB) or (0x0F,0xFF) the CC1101 do not detect it

PS  all my register config :

halRfWriteReg(IOCFG2,0x0D);  //GDO2 Output Pin Configuration : Serial Data Output
halRfWriteReg(IOCFG0,0x06);  //GDO0 Output Pin Configuration : Asserts when sync word has been sent / received, and de-asserts at the end of the packet.
halRfWriteReg(FIFOTHR,0x47); //0x4? adc with bandwith< 325khz
halRfWriteReg(SYNC1,0x55);   //01010101
halRfWriteReg(SYNC0,0x00);   //00000000

halRfWriteReg(PKTCTRL1,0x80);//Preamble quality estimator threshold=16  ; APPEND_STATUS=0; no addr check
halRfWriteReg(PKTCTRL0,0x00);//fix length , no CRC

halRfWriteReg(PKTLEN,38);
halRfWriteReg(FSCTRL1,0x08); //Frequency Synthesizer Control

halRfWriteReg(FREQ2,0x10);   //Frequency Control Word, High Byte  Base frequency = 433.82
halRfWriteReg(FREQ1,0xAF);   //Frequency Control Word, Middle Byte
halRfWriteReg(FREQ0,0x75);   //Frequency Control Word, Low Byte


halRfWriteReg(MDMCFG4,0xF6); //Modem Configuration   RX filter BW = 58Khz
halRfWriteReg(MDMCFG3,0x83); //Modem Configuration   26M*((256+83h)*2^6)/2^28 = 2.4kbps
halRfWriteReg(MDMCFG2,0x02); //Modem Configuration   2-FSK;  no Manchester ; 16/16 sync word bits detected
halRfWriteReg(MDMCFG1,0x00); //Modem Configuration num preamble 2=>0 , Channel spacing_exp
halRfWriteReg(MDMCFG0,0x00); /*# MDMCFG0 Channel spacing = 25Khz*/
halRfWriteReg(DEVIATN,0x15);  //5.157471khz
halRfWriteReg(MCSM1,0x0F);   //CCA always ; default mode RX
halRfWriteReg(MCSM0,0x18);   //Main Radio Control State Machine Configuration
halRfWriteReg(FOCCFG,0x1D);  //Frequency Offset Compensation Configuration
halRfWriteReg(BSCFG,0x1C);   //Bit Synchronization Configuration
halRfWriteReg(AGCCTRL2,0xC7);//AGC Control
halRfWriteReg(AGCCTRL1,0x00);//AGC Control
halRfWriteReg(AGCCTRL0,0xB2);//AGC Control
halRfWriteReg(WORCTRL,0xFB); //Wake On Radio Control
halRfWriteReg(FREND1,0xB6);  //Front End RX Configuration
halRfWriteReg(FSCAL3,0xE9);  //Frequency Synthesizer Calibration
halRfWriteReg(FSCAL2,0x2A);  //Frequency Synthesizer Calibration
halRfWriteReg(FSCAL1,0x00);  //Frequency Synthesizer Calibration
halRfWriteReg(FSCAL0,0x1F);  //Frequency Synthesizer Calibration
halRfWriteReg(TEST2,0x81);   //Various Test Settings link to adc retention
halRfWriteReg(TEST1,0x35);   //Various Test Settings link to adc retention
halRfWriteReg(TEST0,0x09);   //Various Test Settings link to adc retention

  • 0
    TI__Mastermind 36385 points

    Frederic,

    The Sync detection process is based on a correlation engine and correlation engines need the sequence to be as random as possible. This is why we recommend using our default Sync word. However we do enable customer to change it, however when doing so the performance will change.

    To show you the what the correlator results look like for the various Syncwords I have making some pictures for you.

    Here you see all FF's as you can see the "second peak" is only 0.1dB away from from the main peak as that is not good.

    Here is the next one: "0x5500" and here we get 2.2dB signal to noise ratio. Still not good, but not nothing. This is why it does work.

    Now the last one: This is an example of a good sync word. Here we get 12.5dB of signal to noise ratio and is no ramping or other sillyness going on. This is a good syncword. 

    What this story tells you is you need to use a piece of the incomming packet that has some data in it that looks at "random" as possible.

    Hope this helps.

    Regards,
    /TA

  • 0 in reply to TA12012
    Prodigy 20 points

    ok , i better understand  why it is not working , initially i was thinking that is it a kind of "shift and match register", but it look like more complex

    do you plot your diagram like it is done on this thread with xcorr() function ?