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Original question:

MSP430FR5969: SPI/I2C ( Serial) Communication by bit banging method.(MSP430FR5959)

MSP430FR5969: spi/i2c selection criteria

7ACDRIVER
Intellectual 400 points

Part Number: MSP430FR5969

Is there a source document that discusses the criteria for selecting SPI .vs. I2C to drive peripheral off board devices?

  • 0
    Intellectual 995 points

    Hi,

    Perhaps you should try
    www.google.com/search

    Regards,
    Harish KS

  • 0 in reply to Harish Singh
    TI__Genius 17960 points
    Hello,
    unfortunately there is nothing out of the box, which we could offer. But to summarize the most important ones from my point of view:
    I2C pros:
    - requires only 2 GPIOs

    I2C cons:
    - quite complex
    - lower speed
    - requires a higher current consumption due to pull-ups

    SPI pros:
    - simple protocol
    - higher speeds possible, than I2C
    - lower current consumption compared to I2C

    SPI cons:
    - requires more GPIOs (3-4)

    Best regards
    Peter
  • 0 in reply to Peter Spevak
    Intellectual 400 points
    Thank you for the comments - helpful as written, but I am particularly concerned about potential problems with distance between the host and sensor (0.5 to 5m total) and potential noise and signal strength considerations. I was wondering if anyone has measured or quantified these parameters and the cable types and twist rates that work best.
  • 0 in reply to 7ACDRIVER
    Guru 26200 points
    Each bus has its own bus capacity limits.
    Look at those limits and capacities for typical cables.
    If we are talking about meters, consider 1-Wire and RS-232C.
  • 0 in reply to Tomasz Kocon
    Intellectual 400 points
    Unfortunately, RS232 is not an option. The parts I am dealing with support I2C and SPI but not RS232. I have seen offerings for 3m cables for I2c but no performance data related to using that cable. I am still looking for a source of that performance data and any similar data for SPI.
  • 0 in reply to 7ACDRIVER
    Guru 26200 points
    You say: I have seen offerings for 3m cables for I2c
    In other place you mention: distance between the host and sensor (0.5 to 5m total).
    Google may not help.
  • 0 in reply to Tomasz Kocon
    TI__Genius 17960 points
    Hello,
    with such long cables, I would also consider other potential issues, like e.g. with noise immunity versus electromagnetic disturbances, conducted and radiated.
    The generic recommendation would be, to select a communication, or lets say signal transmission standard, which is designed for such cable lengths. I understand, that on the first sight, it might be easier, to go with the communication standard, which is offered by the selected ICs.
    If taking the risk of using not the best suitable communication standard, I see the following main parameters/option to mitigate the risks:
    - Lower the impedance to the allowed minimum, in case of the I2C this would mean using low resistance pull-ups. While of course maintaining the device specification. Here of course also the capacitance needs to be considered.
    - Operate the communication at low data rates, low enough for big margins even with the longest cable lengths
    - Use cables with protective features, like twisted cables, and even shielded ones. Keep in mind the I2C signal topology is not designed for harsh environments. It's not actively driving both high and low phase, and it's also not a balanced signal.

    Please let us know if we can be of further help. In case of no further support need, please verify the answers. Many thanks in advance.

    Best regards
    Peter

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