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F2837xd SPI/SCI baud rate

mosin
Expert 1160 points


Hi

I'm trying to see what throughput I can get from SPI and SCI on the new F2837xd. From the datasheet, I saw that GPIOs maximum frequency is 25MHz. For SPI, maximum clock frequency is LSPCLK / 4. For SCI, maximum baud rate is LSPCLK / 16. With LSPCLK configured to be 200MHz (SYSCLK / 1), theoretically, maximum SPI clock would be 50MHz and SCI would have a maximum of 12.5MHz. Based on the GPIO maximum frequency, SCI would be able to go at 12.5MHz but SPI would be maxed out at 25. On top of that, on the first page of the datasheet, it is written that SPI is high speed at 40MHz. I just wanted to confirm what are the real limitations here. The usage would be to make to F2837xD communicate together using one or both of these communications link.

Thanks!

  • 0
    Guru 30330 points

    Mosin,

    On SPI, there is a High Speed mode supported on a single pin mux option (this will be in the TRM soon) that can achieve 40 MHz. This 40MHz is the max limit of the SPICLK. 

    You are correct that the SCI can theoretically achieve 12.5Mbps. For SCI, you must consider the slew rate of the signal, as long as the data is valid at the sampling points, The SCI will operate. (see Section 18.1.1.7 SCI Communication Format in the TRM)

    Can you tell me where you see the maximum GPIO frequency of 25 MHz?

    I hope this helps! Please don't hesitate to ask anything else.

    Mark

  • 0 in reply to Mark Labbato
    Expert 1160 points

    Hi

    I found the 25MHz thing in the document SPRAAS1B - Hardware Design Guidelines for TMS320F28xx in section 3.4.1. It says that the maximum toggling frequency of a GPIO pin is 25MHz. I think PWM pins on the F2837x can go up to 100MHz so I assume there are different drivers depending on the pins. Does the 25MHz thing applies to the F2837x at all?

    Regards,

  • 0 in reply to mosin
    Guru 30330 points

    Mosin,

    The maximum of 25 MHz in SPRAAS1B will not apply to F2837xD. This doc should be updated in the near future with the latest information. Unfortunately I do not have a date for this yet. 

    The maximum toggling frequency of the GPIOs on F2837xD is 50MHz.

    Thanks,

    Mark