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ads1259 external clock problem~~urgent !

Sung ho Cho
Prodigy 190 points
Other Parts Discussed in Thread: ADS1259, ADCPRO

I designed ADS1259 board using external oscillator, Oscillator, 7.3728 MHZ 3.3V SMD, CTS_CB3LV used in EVM board.

But, value of bit 6 in CONFIGURATION REGISTER 2 doesn't change to1, it keeps value of 0. (xtal2 float, 50ohm series resistor is used)

So, I check the clock using my tektronix oscilloscope, and it works very well.

What's the problem? (I'm a professional acquisition board designer and have used ads1259 for 4 years, and have 20 times more board revision records for ads1259).

  • 0
    TI__Guru* 94335 points
    Sung,


    I don't know of any reasons why the CONFIG2 register would read the clock status wrong. However, there are a few other things to check to make sure.

    Does this happen for a single board or device? Or does this happen on many boards and devices? If this is just a single board, have you tried to replace the device.

    Have you tried to read out other registers? Have you seen any other bad reads in any other registers? Is this an intermittent bad read or does this happen repeatedly.

    Check the CLKIN pin to see if there is a short to another pin or GND. I'd also check to see if there is a bad connection from the oscillator through your 50 Ohm resistor to the CLKIN pin as well. I'd make sure to look at the clock signal at the CLKIN pin directly.

    If you suspect a bad digital read, I'd try to record the read transaction with a logic analyzer. I might be enough to get the SCLK DIN and DOUT readings from an oscilloscope to try to get the reading out.

    Other than that, I would like to see a schematic (or partial schematic) to try to debug this problem.


    Joseph Wu
  • 0 in reply to Joseph Wu
    Prodigy 190 points

    I have tested 5 ADC on 3 different revison board.

    But, register value still does not change. And there is no read error becasue I set other register and read 3 register values together(00~ 02).

    In my results, I think this would ADS1259 chip's own design error..

    Please test your own board and inform your results.

  • 0 in reply to Sung ho Cho
    TI__Guru* 94335 points

    Sung,

    I've tested the EXTCLK bit in the CONFIG2 register and it seems to work fine. It behaves as I would expect and it can be read while in operation. I used the ADCPro software, ADS1259/PGA280EVM and a Saleae logic analyzer to get the read.

    Here is the basic setup. It requires an external +/-10V supply to power the motherboard. I have circled the switch that allows the selection of an external oscillator, or connecting the CLKIN to GND to enable the internal oscillator.

    The ADCPro software does not actively read this register so there is an "Update" button that allows the user to read the CONFIG2 register and get the EXTCLK bit. What I do is switch the clock, capture the bit with ADCPro and use the logic analyzer to capture the data transaction.

    When the switch is turned to GND, the device uses the internal oscillator. I check ADCPro and this is the result I get when I click Update:

    Then I read the logic analyzer to see the data transaction and I read 22h 00h 84h. Bit 6 of the register is 0.

    Then set the switch to OSC so that the external oscillator is set. I update ADCPro and I read that the oscillator is now set to external. I also read the logic analyzer and now bit 6 is a 1. I read 22h 00h C4h.

    It still appears to me that this bit works. I did make some suggestions for testing in my last post. I'd stress that you should measure the oscillator right at the CLKIN pin of the device, just to make sure that the clock is getting to the ADS1259. If you are able to send one, I would look at a schematic and layout.

    Joseph Wu

  • 0 in reply to Joseph Wu
    Prodigy 190 points

    FIrst of all thank you for your great kindness..

    I solve my problem.. At the end, My firmware that I thoght perfect was a origin of problem.

    Because my board is composed  of many isolated multi ADC, I use For loop sentence to get register values, And that of for loop makes a problem..

    It was my fault. 

    To find out origin of troubles, I started with my 1259evm board, and then tested my multichannel board for about over 12 hours long without rest.

    If you don't give me your test results, I still couldn't find problems.

    I sincerely appreciate you.

    Thank you very much.. Have a nice weekend.

     

  • 0 in reply to Sung ho Cho
    TI__Guru* 94335 points
    Sung,


    I'm glad you were able to find the problem. Thanks for reporting back that you have a solution.

    If you have any other questions, feel free to post again.


    Joseph Wu