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Interfacing ADS1248 with MSP430F5438A

Rotem Segev
Prodigy 80 points
Other Parts Discussed in Thread: ADS1248, MSP430F5438A

I am trying to find any hardware related problems with this combination. Here is my simplified schematic.

In the MSP430F5438A I configured P9.0 as output and I keep it low one second after I power the device. P6.2 and P6.3 are configured as general purpose outputs and kept high. I configure SPI1 in the MSP430 using the standard library and I just try to read the internal register values of the ADS1248 but I keep getting zeroes...

the analog inputs are floating and not connected to anything yet.

To my understanding, the communication channel between them doesn't work. I have a clean and stable 3.3V and 3.0V in AVDD and DVDD.

One strange thing I noticed, is that if the DVDD (3.0V) is not present in pin 1 (I turned off the external LDO supplying it) but AVDD is present, I measure a strange 2.3V in DVDD. I don't know if it's related to the communications problem I have.

What could be the cause for this?

  • 0
    TI__Guru* 97585 points
    Rotem,


    There are a few things that I would check if the ADS1248 isn't operating.

    Are you able to write to and read back from the registers of the ADS1248? This is the first step in making sure the communications to the device are correct. I would also verify that the SPI is correct during the read data. Make sure the SPI is correct polarity for the /CS and SCLK.

    I would also verify that there is a clock or that the CLK line is grounded. Based on the schematic, it looks like you've chosen the latter. Then verify that both START and /RESET are both high.

    Based on the schematic, it looks like you have /DRDY set up as a device input instead of an output. Check this connection to make sure that it isn't the MSP430 holding this line low. You could also use the DOUT/DRDY line as long as the device is set up to send /DRDY indication each time a conversion is completed.

    I would also remove the inductor between the AGND and DGND then replace that with a short. Using an inductor between the grounds can cause serious ground bouncing and disrupt communications with the device.

    Other than the above suggestions, I don't see anything that would be a problem with the setup. Your comment about the DVDD appearing to be 2.3V when there is only the AVDD present is not an unexpected result. There are ESD diodes connecting the analog and digital supplies. If there is power on the AVDD line, it will pull up on the DVDD line through one of these ESD diodes.


    Joseph Wu
  • 0
    TI__Guru* 97585 points
    Rotem,


    One last thing: a few of my colleagues noticed that VREFCOM appears to be floating. It should be connected to an AC ground node (through a connection of less than 10Ω).


    Joseph Wu
  • 0 in reply to Joseph Wu
    Prodigy 80 points
    VrefCom was grounded, analog and digital grounds are shorted. We still can't communicate with the ADS1248.
    DRDY is configured as input to the MSP430. As I said, the analog inputs are floating and we just want to establish basic communications with the ADS1248.
    What can be the reason? Are the pins between the MSP-ADS1248 seem to be right?

    Thanks again.
  • 0 in reply to Rotem Segev
    TI__Guru* 97585 points
    Rotem,


    Did you verify the status of the START and /RESET pins? Are you able to make any communications with the MSP430 at all? As I mentioned earlier, the easiest thing to do is to read back from the registers. Once this is correct, then try writing to the registers and verifying the communications by reading back from them again.

    I would get an oscilloscope or logic analyzer and make sure that there is something coming out /CS, DIN, DOUT, and SCLK. If you have an extra line, I'd include /DRDY also. At this point to need to verify that the MSP430 is working the way you think it is.

    Get some sort of screen capture and post it back to make sure the communications is correct.


    Joseph Wu