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DAC81404EVM: SPI Communication Issue Between DAC81404EVM and C2000 MCU (LAUNCHXL-F28P55x)

Ray
Prodigy 20 points
Part Number: DAC81404EVM
Other Parts Discussed in Thread: LAUNCHXL-F28P55X, DAC81404

Tool/software:

Question:
I am integrating the DAC81404EVM with a C2000Tm real-time MCU (LAUNCHXL-F28P55x) via SPI.

When observing the SPI signals with a logic analyzer, the signals SPI_CS, SPI_CLK, and SPI_PICO match the DAC81404 datasheet register configuration. However, SPI_POCI does not return any data (expected DEVICEID: 0x0A60).

The initialization command is:

DAC_write24(DAC_SPI_BASE, 0x03, 0x0A04); // SPI_CONFIG: Enable device // Binary: 0000 0011 0000 1010 0000 0100

With the oscilloscope, I can confirm that SPI_CLK and SPI_PICO are toggling correctly.
It seems that on the DAC81404EVM, some other voltage may be affecting SPI operation, and I am still troubleshooting.

The attached waveforms show:

  1. SPI_PICO Left right arrow DAC_SDI disconnected

  2. SPI_PICO Left right arrow DAC_SDI connected

Has anyone successfully read the DEVICEID from the DAC81404EVM using a C2000 MCU?
Any suggestions on what might prevent the SPI_POCI line from returning data would be greatly appreciated.

  • 0
    Prodigy 20 points

    That is to say, the PICO signal output from the C2000 board is correct, but after connecting it to the DAC81404EVM through jumper wires, the voltage levels become incorrect.

  • 0 in reply to Ray
    TI__Expert 5110 points

    Hi Ray,

    Can you please share a waveform with SCLK, CSz and SDI in single scope frame for the SPI_CONFIG write?
    And also the values of power supplies for the DAC81404 device.

    Thanks,
    Sanjay

  • 0 in reply to Sanjay
    Prodigy 20 points

    1. SPI_PICO  DAC_SDI disconnected

    2. SPI_PICO  DAC_SDI connected

  • 0 in reply to Ray
    Prodigy 20 points

    Hi Sanjay,

    Measured supply voltages (at the device/EVM):

    DVDD: +5.0 V (USB)

    IOVDD: +3.3 V

    Best regards,
    Ray

  • 0 in reply to Ray
    TI__Expert 5110 points

    Hi Ray,

    Thanks for the details. I see that once you connect the DAC_SPI, the data line is not stable during the SCLK falling edge. Can you please debug this first?

    You can take help from the C2000 team for that. 

    Thanks,
    Sanjay

  • 0 in reply to Sanjay
    Prodigy 20 points

    Hi Sanjay,

    You’re right—that’s exactly the issue I’ve been chasing. With the DAC81404 EVM connected, the SDI (MOSI) level isn’t stable around the SCLK falling edge; when the EVM is disconnected, the waveform is clean. I suspect contention or loading on the SPI lines.

    Thanks again for the pointer—any additional tips are appreciated.

    Best regards,
    Ray