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CC1020 in synchronous receiver mode - dclk is not triggered

F�vero Santos
Intellectual 385 points
Other Parts Discussed in Thread: CC1020

Hello, all

I am working with CC1020 radio transceiver and I observed a characteristic in my receiver: when receiving data, my DLCK is not triggered in a constant frequency. I say that because my transmitter DCLK is triggered at 5k Hz frequency.

Reading the CC1020 datasheet I observed that I should use DCLK as an interrupt input (to my msp). Actually, I'm not using it as an external interrupt because the pin in which the DIO is connected in my microcontroller does not support external interruptions. What I did was setting up a timer to interrupt at 9,5K Hz frequency, sampling the states of DCLK pin and then fetching the data (this worked well for the TX side).

So my doubts are: Why is the DCLK clock in RX mode is not constant as it is in TX mode? A not constant clock in RX mode is a normal operation (and that's the reason why datasheet says I should use external interruption)? Or am I forgetting something when configuring RX mode?

Thank you for your help.

Fávero 

  • 0
    TI__Guru**** 317180 points

    Could you post a plot of how DCLK looks like? From your description I'm not sure what you mean by "not constant"

  • 0 in reply to TER
    Intellectual 385 points

    Hello

    By not constant I mean DCLK from RX side is not exactly 5k Hz as it is in TX side (TX and RX are separeted devices, a server sending data and client receiving).

    I can note this difference because I've triggered my scope into those signals and compared them.

    Thank you


    Fávero

  • 0 in reply to F�vero Santos
    TI__Guru**** 317180 points

    For weaker signals the DCLK signals will have some jitter due to internal oversampling effects etc. Is it this you are seeing? That is why I asked about a plot showing the signal since "not exactly 5 kHz" is not an accurate description.

  • 0 in reply to TER
    Intellectual 385 points

    Hello, TER

    Thanks for the reply. Yes, it was jitter in the DCLK but it was way a too strong interference... Now it seems OK, I changed some register values and apparently I'm good to go. There's other characteristic I would like to discuss: When receiving data, an eventual high peak signal shows up in my DIO output (I can verify it with scope). I just want to know what are those eventual low to high transitions my receiver eventually get when I'm not even transmitting data.

    Thank you

  • 0 in reply to F�vero Santos
    TI__Mastermind 39860 points

    F���vero Santos said:
    When receiving data, an eventual high peak signal shows up in my DIO output (I can verify it with scope). I just want to know what are those eventual low to high transitions my receiver eventually get when I'm not even transmitting data.

    My understanding is that you see random data on the RX DIO pin even if no data is being transmitted. This is to be expected as the receiver will be demodulating noise when there is no signal present at the antenna. One thing to try is to set INTERFACE.DCLK_CS = 1. DCKL and DIO will then  not start running before there is a signal a the antenna above a pre-defined level (carrier sense threshold). Refer to section 12.11 in the CC1020 datasheet for details on how to set the carrier sense threshold.

  • 0 in reply to Sverre
    Intellectual 385 points

    Thanks! This actually answers my next question :)