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Starterware/TRF7961: TRF7961 SPI

mike zeng
Intellectual 470 points
Part Number: TRF7961

Tool/software: Starterware

SPI FOR TRF7961

hello EXPERT,

I have the question to confirm with you on SPI OF TRF7961,now I attach one ppt to show detail information,please answer me based on it;TRF7961.zip

thanks a lot.

  • 0
    TI__Guru*** 131400 points

    Hello Mike,

    I am going to assume that the MISO line is also shared even though not indicated in your PPT.

    1) Yes
    2) TI Recommendation is to use tri-states for MISO, MOSI, and SCLK. It may be possible to only do MISO if the TRF7961 is DISABLED by pulling EN=LOW during other SPI transactions, but there is no precedent for doing. Again, recommendation is Tri-state buffer on each of MISO, MOSI, and SCLK.
    3) Yes this is specific to the TRF7961. It is due to the chip design.
    4) I did not make this decision, my best guess is it is not considered a specification and thus not included in the DS.
    5) We do not characterize the likelihood of such behavior. We simply are explaining the device behavior so you understand the risks. If you choose to ignore TI recommendations, then it is up to you validate your products functionality and take the RISK that your product may malfunction at some point.

  • 0 in reply to Ralph Jacobi
    Intellectual 470 points

    hello Ralph,

    add one information:MISO line is only used to TRF7961,not shared to other device.

    is there any difference?

    thanks.

  • 0 in reply to mike zeng
    TI__Guru*** 131400 points

    Hello Mike,

    If MISO is not shared with other devices, then I don't see any need for a tri-state buffer on it. As far as MOSI/SCLK go, I stand by what I said in the answer to question 2 above which I will reword for clarity:

    2) TI Recommendation is to use tri-state's for MISO, MOSI, and SCLK. It may be possible to not apply tri-state's to MOSI/SCLK if the TRF7961 is DISABLED by pulling EN=LOW during other SPI transactions, but there is no precedent for doing. Again, recommendation is Tri-state buffer on MOSI and SCLK.

  • 0 in reply to Ralph Jacobi
    Intellectual 470 points
    HELLO Ralph,
    it should be:MOSI not MISO ,right?

    Again, recommendation is Tri-state buffer on MISO and SCLK.
  • 0 in reply to mike zeng
    TI__Guru*** 131400 points
    Hello Mike,

    Yes, sorry. I edited my original post to reflect this as well.
  • 0 in reply to Ralph Jacobi
    Intellectual 470 points

    hello Ralph,

    can you tell me what's negative impact when the tri-state buffer is not used? Does it impact RFID controller itself, for example, does it impact RFID communication between controller and RFID tag?

    or it will impact other device in the same SPI bus?

    thanks.

  • 0 in reply to mike zeng
    TI__Guru*** 131400 points
    Hello Mike,

    In theory, both.

    If the TRF7961 receives a command it can process, it would process it and attempt to reply if the command would cause such a behavior. Such a reply would impact other devices on the SPI bus. Furthermore, if it processes a command, then it could impact the communication between the transceiver and an RFID tag.

    If the TRF7961 receives a command it can't process, in theory nothing should happen, but this has never been tested or qualified and I can't say with any certainty that after receiving many such commands the device could be put into a bad state. If that occurs, it would also impact the communication between the transceiver and RFID tag.
  • 0 in reply to Ralph Jacobi
    Intellectual 470 points
    hello Ralph,
    to be brief, if the tri-state buffer is not added, will the SPI to RFID controller have some problem or not? I think it must impact other SPI device,but not sure that it will impact RFID controller;
  • 0 in reply to mike zeng
    TI__Guru*** 131400 points
    Hello Mike,

    I've said this before: "We do not characterize the likelihood of such behavior. We simply are explaining the device behavior so you understand the risks. If you choose to ignore TI recommendations, then it is up to you validate your products functionality and take the RISK that your product may malfunction at some point."