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GPIO Pullup/Pulldown values on Am335x

b.buettner
Prodigy 150 points


I'm going to drive the 'program' pin of a FPGA with GPIO3_19. This signal must be at high level during powerup. Powerup for this pin is High-z with activ pulldown. So I have to install an external pullup. Because nowhere the value of the internal pullup/pulldown resistors is defined I don't know the needed value of the external pullup. What value must an external pullup-resistor have to generate a valid high level against the internal pulldown?

  • 0
    TI__Guru**** 393215 points
    Hi Bernd,
     
    The pullup/pulldown values can be found from AM335X Datasheet Table 3-11. Look for the parameters "Input leakage current, Receiver disabled, pullup/pulldown enabled". Also bear in mind that the I/O cells are dual voltage and work ether at 1.8V or 3.3V supply.
  • 0 in reply to Biser Gatchev-XID
    Intellectual 425 points
    Hi,

    Excuse me for hijacking this old thread, but your answer got me curious. I currently have a problem with an existing PCB that has a missing level converter for two signals. The peripheral have a 1.8V input and the AM335x have 3.3V outputs.

    I have not found anything about the I/O cells (if you by that mean the I/O-s of AM335x) being dual voltage in the data sheet of AM335x, but if they are it would totally save my day!
  • 0 in reply to Jonatan Magnusson
    TI__Guru**** 393215 points
    Yes, the I/O cells of AM335x are dual-voltage, but this is fixed, i.e. they operate either at 1.8V or 3.3V, depending on the VDDSHVx voltage, which powers the I/O cell. This can be see in Table 4-1 from the AM335x Datasheet Rev. J.
  • 0 in reply to Jonatan Magnusson
    Prodigy 150 points

    Hi,

    all I/O pins of the Am335x belong to a specific power-domain. If a power domain is powered mit a 1.8V regulator, the I/O pins has 1.8V characteristics, i.e. it drives 1.8V. The output voltage cannot be changed by software. So in an existing design you have a problem. One possibility is to define the output as tristate, disable pullup/pulldown and give it an external pull-up to 1.8V. For a low-level you drive the output low, for a high-level you set the pin to tristate. Never drive the output high.

    Bernd

  • 0 in reply to b.buettner
    Intellectual 425 points
    Thanks Biser and b.buettner! b.buettners hint was a fantastic workaround for my problem, and it seems to work flawlessly!