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F28377D Boot Pins and SCI

Cem Koose
Intellectual 880 points

Hi,

GPIO72 and GPIO84 is boot pins of the f28377d. Also gpio84 is shared by SCIA. I'm using gpio84 pin as SCI. Normally I use 10k pull-up resistor and 100nf filter cap at boot pins. It is important to filter noise on the boot gpios to provide a clean boot selection at the start-up. Since gpio84 is also used for the SCIA, are there any design tip about this design which uses same pin for boot selection and SCI. Or are there any issue reported about this type of application? I removed the filter cap from gpio84 to ground, so now there is only pull-up resistor.


Regards,

  • 0
    TI__Mastermind 42195 points

    After digging around a bit I would recommend a 4.7k or a 10k pull-up on this pin. It's generally not a good idea to filter on a transceiver. However, if needed its best to place the filter on the receiver side. Let me know if you have any other questions!

    Thanks,
    Cody

    -If the question has been answered please mark it as such.

  • 0 in reply to Cody Watkins
    Intellectual 880 points
    Hi,

    I'm using 10k on GPIO84 and 72. I removed capactior from GPIO84(SCI_TX). I can upload code using SCI boot using C2Prog software. Default SCI-Boot uses SCITXDA: GPIO84, SCIRXDA: GPIO85 pins. May be for low communication speed a couple of nf can be used on GPIO84(SCI_TX).
    After programming process, cpu boots from flash through get mode. In this case pull-ups are used in gpio84,72.

    Regards.
  • 0 in reply to Cem Koose
    TI__Mastermind 42195 points

    You should be able to include a few nf's. Just be sure that the filter's cutoff frequency is high enough to allow the fastest baud rate that you expect to use. Also, don't forget to add some margin!

    Regards,
    Cody