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TMS320F28377D: SPI clock waveform distortion

Leo Wu
Intellectual 1360 points
Part Number: TMS320F28377D

Tool/software:

Hi customer,

My customer is using 28377D to develop SPI function (master mode). They configured the SPI clock frequency to 40MHz and found that the clock waveform is abnormal.

The frequency is 40MHz, but the waveform is not the trapezoidal wave. At this time, the SPI communication is abnormal.

I asked them to test the SPI communication at the lower frequency: 25MHz. The clock waveform seems normal.

I check the datasheet of 28377D. it says that the max toggling frequency of GPIO is 25MHz.

However, the SPI timing says that the max frequency of SPI clock is 40MHz (25ns) or 50 MHz  (20ns)

Does 28377's GPIO has a high speed output mode to support 40MHz clock output?

Any suggestions for this issue?

  • 0
    TI__Mastermind 23300 points

    Hello,

    High Speed SPI mode (up to 50MHz) is supported on this device. The only requirements to use SPI at this speed is to ensure you are using the correct GPIOs that can support it (and you enable high speed SPI mode in the SPI module configurations). The typical GPIOs support up to 25MHz, but dedicated GPIOs can support high speed SPI as described in the device datasheet:

    Best Regards,

    Allison

  • 0 in reply to Allison Nguyen
    TI__Intellectual 1360 points

    Hi experts,

    My customer use HS_MODE and use the GPIO65 to output SPI clock.

    But the clock waveform is abnormal.

     SPI clock: 33MHz

    SPI clock 50MHz:

    SPI configuration

    As a comparison, SPI clock 25MHz (normal):

     

    Thanks,

    Leo

  • 0 in reply to Leo Wu
    TI__Mastermind 23300 points

    Hi Leo,

    If the SPI module itself is working ok, you are using High Speed GPIOs, and the clock looks fine at other speeds, then it seems to me the SPI module is functioning fine. Are your GPIO setups the same as how our examples initialize the SPI GPIOs?

    Please double check the scope/probe that are being used to measure the clock signal as well and any SPI hardware connections.

    Best Regards,

    Allison

  • 0 in reply to Allison Nguyen
    TI__Intellectual 1360 points

    Hi Allison,

    You means we have a high speed SPI demo?

    Thanks.

    Leo

  • 0 in reply to Leo Wu
    TI__Mastermind 23300 points

    Hi Leo,

    If the SPI is able to transmit and receive fine, and the only concern is the appearance of the SPI clock pulses, this is likely a result of hardware connections- hence why I suggested checking your scope settings/equipment and any resistor or capacitor connections. 

    Is the function of the SPI at 40MHz (transmitting and receiving) working ok? Are you also scoping out the other SPI lines to see if data is able to be sent and transmitted? You can also try internal loopback mode to verify if the SPI module configurations are correct when transmitting and then receiving back the same data.

    Best Regards,

    Allison