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DAC80508: SPI SDO Missing

user5941200
Prodigy 40 points
Part Number: DAC80508

Hi team,

I would like to know whether there's any operation I need to do before I sending read / write SPI commands to operate DAC80508?

I tried to read DAC80508 register DEVICE ID register by issuing 0x82, 0x00, 0x00, and trigger another data cycle after 1ms for retrieving read result, as figure below.

However, I got nothing while I issuing second data cycle, what might go wrong?

The operating conditions is as below:

VDD = 5.0 , VIO = 3.0V, Temperator = 25°C

  • 0
    TI__Genius 14220 points
    Hello,

    Welcome to E2E and thank you for your query. Your waveform looks fine. I have a few questions and suggestions:

    1. Have you tried writing to the DAC and seen it work? For example, writing any code to the DAC? If it's not working, there might be some issue either with the connection or the device. Try measuring the signals close to the DAC pins and check the connections
    2. If SPI write is working, try reading continuously and check if SDO is toggling or not.
    3. Please also share your schematics (the DAC portion) if possible

    Regards,
    Uttam Sahu
    Applications Engineer, Precision DACs
  • 0 in reply to Uttam Sahu
    Prodigy 40 points
    Thanks a lot for your reply.

    Seems like there's on operation I need to do before sending read / write SPI commands after Power-on-reset, am I right?

    And from your suggestions, what I did is:
    I've tried to write DACx registers (0x8 to 0xF) to zero through SPI commands and the output voltage weren't changed.
    By the concern on connection, I've tried to measure the signal directly from the DAC pins and got the same results.
    And from your concern on the device issue, I tried another DAC80508 IC, and the same, nothing happened after my read / write operations ..
  • 0 in reply to user5941200
    TI__Genius 14220 points
    Hi,

    I tested it on the DAC80508EVM using the GUI. I read back the DEVICE ID without any other operation before and it read the values properly. As you are not able to perform the write operations as well, it might be a good idea to review the circuit. Please upload the DAC portion of your schematic.

    Regards,
    Uttam
  • 0 in reply to Uttam Sahu
    Prodigy 40 points

    Hi Uttam,

    After posting this question, I bought a DAC80508EVM too and got it these days, and it works correctly with GUI.

    And I finally found that I might get DAC80508C rather than DAC80508 since I found the SDO pin behaves like the CLR pin.

    For another problem on failing to writing DAC is due to the SDI pin is interfered by other pins.

    So I have few questions about DAC80508C:

    1. If there's no SDO pin, there's no read operation so we are not able to get the registers' state, right?

    2. And further, how does error checking work on DAC80508C?

    Thank you so much for your help!

  • 0 in reply to user5941200
    TI__Genius 14220 points
    Hi,

    Apologies for the delay.

    Without the SDO pin, register read is not possible. So, it's a trade-off for pins depending on whether you need the read functionality or the CLR functionality.

    When the SPI timings are set properly as per the datasheet, error in communication is very rare. If the application is DC, you can write twice for minimizing the error probability. But, you're right that there is no absolute error check possible after the write operation.

    Hope that answers your question.

    Regards,
    Uttam
  • 0 in reply to Uttam Sahu
    Prodigy 40 points

    Ok, thanks a lot for your help!