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Boot Mode Selection GPIOs Set UP on TMS320f28335

Fikadu Degefa95
Intellectual 350 points
Other Parts Discussed in Thread: TMS320F28335

Hello all,

I have two doubts.

1. I am working on TMS320F28335.  I tried to set GPIO84- GPIO87 in order to select a boot mode selection. But, I couldn't debug in pulling up those pins. later I just floated (Removed the resistors)those pins and it is working properly now. Does it matters if I leave it as it is? i.e without  Boot mode selection resistors

2.  when I use an External ADC Reference voltage of 2.048, what would be a digital value computation? is it  DigitalValue = (4095*AnalogValue)/3 or DigitalValue  =(4095*AnalogValue)/2.048 ?

 Any one help me would be appreciated.

Thank you very much inn advance

  • 0
    TI__Guru 61235 points

    Fikadu,

    1. All four bootmode pins have internal pullups on them which are active by default.  This gives jump-to-flash boot mode.  Typically you don't want to just rely on these, as the internal pulls are weak.  To ensure a good boot mode selection even in noisy operating environments, 10K to 4.7K external pull resistors should be used to set the boot mode.  I'm not sure what you mean when you say "I couldn't debug in pulling up those pins."

    2. Full-scale range of the ADC is 0 to 3V regardless of what is used for the reference.  There is a register that you set that identifies the reference being used.  The ADC adjusts for this and delivers a 0 to 3V full-scale range.  So:

    DigitalValue = (4095*AnalogValue)/3

    always.

    The motivation for using an external reference is to get better temperature stability.  It does not change the ADC range.

    Regards,

    David

  • 0 in reply to David M. Alter
    Intellectual 350 points

    Dear David,

    I would like to pay a huge respect for your help.

    I am fully satisfied with the answer. Thank you very much