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Problem in Receiving POCSAG by CC1101

M Khani
Prodigy 70 points
Other Parts Discussed in Thread: CC1101, CC1120

Hi

I'm working with CC1101 to receive POCSAG messages (f=452.6MHz, Baud=1200, Ch=25KHz, Dev=4.5KHz).

CC1101 is configured with 2-FSK, FREQ=452.599792MHz, CHANSPC=25.39KHz, DRATE=1.19948kBaud, DEVIATN=4.364KHz, CHANBW=58KHz, FREQ_IF=457KHz, No Preamble/Sync, No CRC, .

RX FIFO and Important Status registers are polled at nearly 4-times the baud rate and sent to a serial port on a PC. During the whole packet reception, RX FIFO=0xFF, FREQEST=0x09, LQI=0x80, RSSI~0xE2 as can be seen below:

FREQEST LQI RSSI State PKTS RXB RX
9 80 DE 0D E2 1   
9 80 E6 0D E2 1   
9 80 E2 0D E0 2 FF
9 80 DD 0D E2 1   
9 80 E6 0D E2 1   
9 80 E3 0D E0 2 FF
9 80 E5 0D E2 1   
9 80 E3 0D E2 1   
9 80 E6 0D E0 2 FF
9 80 E2 0D E2 1   
9 80 E4 0D E2 1   
9 80 E1 0D E2 2 FF

What's the problem with the data? Which configuration is wrong?

Thank you in advance

  • 0
    TI__Mastermind 36395 points

    Khani, 

    If you disable the Sync word detection the CC1101 has no reference to grab the rest of the payload. Therefore, I would considder it expected performance that it does not work. Can you post the packet format that you are trying to receive and I can be more helpful on what I would recommend.

    Regards,
    /TA

  • 0 in reply to TA12012
    TI__Mastermind 36395 points

    I lookup the Sync word use in. For the CC1101 you can only use the two first words as the CC1101 only supports 16 bit sync word. The CC1120 can support 32 bit sync words.

    Then you need to make the packet length very long (not sure how long) and then start pulling data out of the FIFO during the Reception of the packet.

    Regards,
    /TA

    FCS = 01111100110100100001010111011000
     Sync word 0 Sync word 2 Sync word 3 Sync word 4
    01111100 11010010 00010101 11011000
    7C D2 15 D8
  • 0 in reply to TA12012
    TI__Guru**** 317180 points
    Polling registers is not a good solution. As I wrote in the thread you originally posted in you can use sync or async serial mode and do post processing on the mcu side.
  • 0 in reply to TA12012
    Prodigy 70 points

    Dear TA12012

    Thanks for your comments. The problem was related to frequency offset. While a commercial FSK transceiver receives POCSAG messages at 452.6MHz but the CC1101 module receives at 452.6MHz+32KHz! Now the problem is corrected by frequency offset correction.

    Thanks again