AD7763 Filter Download Question

Hi,

 

I am having problems downloading filters to the AD7763. I have tried the example in the datasheet (in Table 16) so that I know the checksum is correct but I am not getting the FILTER_OK or DL_OK bits set in the Status read (the other bits of the Status read are fine - and UFILTER is set).

 

I am convinced that I have no problems with the data timing and I have a good clean clock, frame sync and data. I am clocking at 12.8 MHz.

 

I would be grateful for answers to the following questions:

 

1. Are there are any errors or omissions in the datasheet with respect to the download?

2. Is there any difference between the effects of applying a hardware SYNC (via the SYNC pin) or writing to the SYNC bit in Control Register 1?

3. In Table 16 it is not clear whether the delay for the checksum should be before or after writing the checksum, could you clarify this please?

 

Many thanks,

 

Gary Moore

  • Hi Gary,

    I have exactly the same problem as you.

    I want to download a fir to the AD7763. I try to download a complete FIR without success.

    So, I test the example in the datasheet (table 16) and I have the same results than you (filter_ok and dl_ok are not set).

    I have tried more than 20 tests with/without delay between coeff/checksum, etc and it doesn't work.

    nOw, I have no idea to resolve this critical issue.

    Did you find a solution ?

    It would be great if somebody can answer quickly.

    Thanks a lot for any response.

    François

  • Hi Francois,

     

    Sorry for the delayed reply. Unfortunately I haven’t solved the problem, I got around it by implementing the filter in software – probably not a lot of help to you, sorry.

     

    I suspect that my problems may have been because my SYNC pulse wasn’t long enough but I’m not sure. I may have another look at it later but it’s a low priority for me now as I have the software work-around and I have other aspects of the system that I need to sort out.

     

    Very sorry that I can’t be more helpful. If you do find the answer I would be interested to hear.

     

    Regards,

    Gary

  • 0
    •  Analog Employees 
    on Oct 21, 2013 3:44 AM

    Hi,

    We are looking into this. As of the moment, can you provide details on the settings of your MCLK div?

    On the AD7763 Evaluation board we are set up with an MCLK = 40MHz, CDIV= 0, and SCR = 0. This means that the SCO frequency = 20MHz and the internal clock frequency used is 20MHz.

    With this default we are able to repeatedly download the coefficient example from the datasheet successfully. And we visibly see that the noise floor of our the FFT of our conversions changes as a result.

    Thanks and Best Regards,

    Chris

  • Hi Chris,

    My configuration is as follows:

    I have 4 AD7763s running together using MCLK = 25.6 MHz and with CDIV = 0 so that ICLK = MCLK/2 = 12.8 MHz.

    We have the decimation set to x16 so our output sample rate is 100 kHz.

    In an earlier version of our design we were running with CDIV = 1 and I’m fairly sure that this worked OK, i.e. we could successfully download the filter. Unfortunately it is not straightforward to re-create that arrangement.

    As I said in my response to Francois, it's possible that my problems are caused by the SYNC pulse width as we discovered that it wasn't as wide as we intended. I have not tried the download since we fixed that but I will let you know if this is successful.

    Thanks,

    Gary

  • Hi Gary,

    After responses from Analog Devices engineers this friday, i succeed to download the 12 defaut coeffcient described in table 16 of datasheet.

    My problem was a bad configuration. I used CDIV = '1' and SCR = '0'.

    Unfortunately, to download the coefficients, it must be CDIV = '0' and SCR = '1' or CDIV = '0' and SCR='0'.

    After that, all status (dl_ok, filiter_ok , ...) was ok.

    I hope this is help you.

    Best Regards

    -----------

    François NORMAND