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TMS320F28379D: Maximum length of SPI bus at 40 Mbps

Thuan Duong
Intellectual 455 points
Part Number: TMS320F28379D

Hello TI officers,

I am working on a project where I establish SPI communication between 2 TMS320F28379D Delfino Boards. I am configuring the SPI to run at High Speed Mode, 40 Mbps ( as in the TMS320F2837xD Dual-Core Delfino Microcontrollers - Technical Reference Manual document, p.912, 40 Mbps is the maximum baud of SPI). The program works fine if SPI wires are short, around 15 - 20 cm, but it doesn't when I tried increasing wire length to 50cm - 100 cm, all data transmitted are wrong. May I ask what is the maximum allowable cable length of SPI bus ? Does the length depend on any other factors, like the baud rate of SPI, voltage level at the transmitter/receiver ? And how can I account for them ? 

Regards,
An.

  • 0
    TI__Mastermind 45166 points
    Hi Thuan,

    SPI is typically used for short distance communications and there is a speed/distance trade off as you'd expect. We don't specify a "maximum wire length" to use since there are a lot of factors that can go into this. If your interface is clean enough, and allows the timing parameters within the device datasheet to be met, then your communication will be successful.

    One assumption that is made in the datasheet is "All timing parameters for SPI High-Speed Mode assume a load capacitance of 5 pF on
    SPICLK, SPISIMO, and SPISOMI."

    If you're wanting to better your SPI bus interface and make it more clean, a number of resources should be available online on the subject. There's a TI document on "Extending the SPI bus for long-distance communication" linked below, howeverI don't think it's for High-Speed mode specifically.

    www.ti.com/.../slyt441.pdf

    Hope this helps,
    Kevin
  • 0 in reply to Kevin Allen18
    Intellectual 455 points
    Thanks Kevin, that helps.