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CC2745R10-Q1: The SPI Timing

Long Li
Prodigy 20 points
Part Number: CC2745R10-Q1

Tool/software: 

I used the SPI interface on the CC2745 chip, and I downloaded the SDK from the TI website. The SPI operated in master mode (SPH=1, SPO=1). However, there were some differences in the datasheet: the minimum value of tCS. LEAD is 1 SCLK, but the actual value was 0.5 SCLK; and the minimum value of tHD.CO is 0 ns, but the actual value was -2.4 ns (the PICO change before the SCLK).

I have the following questions:
1. Does it have any impact on the SPI communication if tCS. LEAD and tHD.CO are not the same as in the datasheet?
2. Can I modify the tCS. LEAD and tHD.CO values in the SDK, and if so, how can I do it?
  • 0
    TI__Intellectual 2570 points

    Hi 

    I am not sure I understand your question correctly. Because I read your capture, it looks like, from CS falling edge to first clock falling edge is 0.5us which equals t spi / 2 . t spi here is 1us. SCLK should be 0.5us because the length between CS falling edge and low or high lasting time in SPI clock is the same  

  • 0 in reply to Barbara Wu
    Prodigy 20 points

    Hi

       The SCLK I am using has a cycle time of 1 µs, and the measured tcs.LEAD time is 0.5 µs. Does this mean that tcs.LEAD does not comply with the reference design? According to the reference design, the minimum tcs.LEAD should be 1 SCLK, but the oscilloscope measurement shows only 0.5 SCLK. Will this discrepancy between the tcs.LEAD time and the reference design affect SPI transmission? How should I adjust it to meet the reference design requirements?Since I am using the SPI driver within the SDK, how should these timing configurations be set?

  • 0 in reply to Barbara Wu
    Prodigy 20 points

    Hi Barbara

         Our project is currently quite urgent. Could you help follow up on this issue? If there are any additional measurement data that need to be provided, please let me know. Alternatively, if there are any questions regarding the issue, feel free to share them with me. If you're currently busy and unable to handle this, could you help find an engineer to provide clarification?
    Thank you.

  • 0 in reply to Long Li
    TI__Intellectual 2570 points

    So we need to understand SCLK definition. What is your SPI frequency setting? And is SPI in controller role? Here it seems t SCLK_H/L = t CS.LEAD. 

  • 0 in reply to Barbara Wu
    Prodigy 20 points

    Hi Barbara

          I previously uploaded a screenshot—can you see it on your end? I am using an SCLK of 1 MHz, which means the period is 1 µs. The SPI is operating in Controller mode (SPH=1, SPO=1). However, the tcs.LEAD I measured is different from what is specified in the datasheet. Since I am using TI's SPI driver.The SCLK_H/L is originally defined as 0.5 SCLK, so when you mention that SCLK_H/L is equal to t_CS.LEAD, I’m unsure whether this is a coincidence or a result of driver settings. My current concern is that t_CS.LEAD does not match the range defined in the datasheet.I now have the following questions and would appreciate your assistance:

    1. What impact does the discrepancy between tcs.LEAD and the datasheet have on SPI communication?
    2. How can I adjust the timing of tcs.LEAD in the software?
    3. Do you have any documentation on adjusting SPI timing that you could share?

    Here are some annotated images I created for your reference. The first one shows the oscilloscope measurements of CS and SCLK, while the second and third images are screenshots taken from the datasheet.

  • 0 in reply to Long Li
    TI__Intellectual 2570 points

    Hi Long,

    I see similar results as you have. I don't think there is SPI function problem on your side. What is your concern? Besides I am checking internally for content which needs more time to get back.

    Best Regards,

    Barbara

  • 0 in reply to Barbara Wu
    Prodigy 20 points

    Hi Barbara

        I am currently concerned about the SPI timing not aligning with the datasheet specifications, which might pose potential risks. I believe the datasheet specifies the minimum tcs.LEAD for a reason reason. Although no obvious transmission errors have been detected so far, the timing discrepancy with the datasheet remains a concern. I am particularly worried about potential issues that may arise in the future.

    Best Regards

    Ron

  • +1 in reply to Long Li
    TI__Intellectual 2570 points

    Hi Long,

    There is no function issue of SPI, the spec content in datasheet has mistake, we will update it shortly.

    Best Regards,

    Barbara