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TMS320F28022: About GPIO status at power on of the device

Koichi Ie
Intellectual 270 points
Part Number: TMS320F28022

Hello,

I have a question about GPIO operation at power on.

When using the LaunchPad (LAUNCHXL-F 28027), GPIO pin was pulled up externally and the 3.3 V power was turned on,
the following phenomenon was confirmed.

1. which goes "High" immediately after the power is turned on.
    GPIO0, GPIO1, GPIO2, GPIO3, GPIO4, GPIO5, GPIO6, GPIO7 GPIO12, GPIO18, GPIO28, GPIO29

2. Immediately after turning on the power supply, it goes from "High" to "Low" and goes "High" after about 5.8 usec.
    GPIO19, GPIO34

* It is unconfirmed about GPIO16, GPIO17, GPIO32, GPIO33.


Since I am concerned about outputting "Low" at power on, please tell me about the followings.

1) Is there sometimes a low output at power on?
2) Which pin outputs Low at power on?
3) What is the timing (or state) and how long is it to become Low?


Best Regards,
Koichi

  • 0
    Guru 192875 points
    Hi,

    Check this in-depth wiki page and article: processors.wiki.ti.com/.../General_Purpose_IO_(GPIO)_FAQ_for_C2000

    Regards,
    Gautam
  • 0 in reply to Gautam Iyer
    Intellectual 270 points

    Gautam-san,

    Thank you for your quick response.


    Sorry. One more thing, there is a condition.

    Immediately after Power-On Reset period(XRS=Low), the external pull-up GPIO is Low is observed.
    The phenomenon is confirmed, the GPIO19 and GPIO34 it.


    Please refer to the waveform (scale-up, scale-down), which was observed as a representative of the GPIO19.

    Please refer to the waveform when the GPIO0 is pulled up externally as a comparison with GPIO19.

    Is it a specification to become low immediately after power on?


    Best Regards,
    Koichi

  • 0 in reply to Koichi Ie
    Intellectual 270 points
    Hello,


    additional information.

    · When pullup with a 2.2K resistor attached, it is confirmed that GPIO19, GPIO34 goes low immediately after
    turning on the power supply. (It is a phenomenon during the question)

    · When pullup with GPIO19 and GPIO34 connected externally, it did not become Low when pullup without resistance.


    I will change the question.

    1. Is there a problem with measures to pullup the GPIO without resistance?
    2. Is there GPIO applicable other than GPIO19 and GPIO34? (The target is F2802x series)


    Best Regards,
    Koichi
  • 0 in reply to Koichi Ie
    TI__Mastermind 42195 points

    Koichi-san,

    what software is loaded on the device? It is possible that the user's code is affecting the state of the GPIO and causing these glitches.

    Please try to use WaitBoot mode and see if the behavior is still the same.

    I don't know of any problems with using pullups this way, I will inquire about this.

    Could you show a simple circuit of how the pullup has been connected? I want to check this so that we don't have any miscommunications.

    Regards,
    Cody

  • 0 in reply to Cody Watkins
    Intellectual 270 points

    Cody-san,

    Thank you for your reply.

    It was my misunderstanding about the behavior of the pull-up without resistance.
    Please close the question about resistance-less pull-up.

    Let me check the following phenomenon about factors that occur in a specific GPIO.

    What I would like to confirm is that it seems that "Low" is output as though the device is pulled up
    externally at 2.2 kΩ immediately after power is turned on.

    Because it is right after power-on, it is thought that XRS = Low and before software execution.
    To confirm the phenomenon, GPIO19 of the launch pad of F28027 is pulled up with 2.2 Ω.
    GPIO19 is not connected except pull-up.

    Refer to the attached circuit diagram.

    Best Regards,
    Koichi

  • 0 in reply to Koichi Ie
    TI__Mastermind 42195 points

    Koichi-san,

    I will run some tests tomorrow. Could you please test something for me?

    1. Disconnect the power from the LaunchPAD
    2. Press and hold S2
    3. Connect the power
    4. Release S2

    When following these steps do you see the same behavior with GPIO19 and GPIO34?

    Regards,
    Cody

  • 0 in reply to Cody Watkins
    Intellectual 270 points
    Cody-san,

    Thank you for your support.

    My confirmation procedure is as follows.

    1) Disconnect the power from the LaunchPAD
    2) Connect GPIO19 to external power supply line of 2.2 kΩ for external pull-up
    3) Connect oscilloscope probe to VCC (3.3 V), GPIO19, XRS
    4) VCC (3.3 V) as a trigger and set the single trigger mode
    5) Connect the power

    Reset from S2 is not used. It is only reset by POR.


    Best Regards,
    Koichi
  • 0 in reply to Koichi Ie
    TI__Mastermind 42195 points

    Koichi-san,

    thank you for the help with this debug. This behavior is do to power sequencing when using the internal voltage regulator. You can find several descriptions of this behavior in the DataSheet. Please see the quote below.

    "

    NOTE: When the on-chip VREG is used, the GPIO19, GPIO34, GPIO35, GPIO36, GPIO37, and GPIO38

    pins could glitch during power up. If this is unacceptable in an application, 1.8 V could be supplied

    externally. Alternatively, adding a current-limiting resistor (for example, 470 Ω) in series with these pins

    and any external driver could be considered to limit the potential for degradation to the pin and/or external

    circuitry. There is no power-sequencing requirement when using an external 1.8-V supply. However, if the

    3.3-V transistors in the level-shifting output buffers of the I/O pins are powered before the 1.8-V

    transistors, it is possible for the output buffers to turn on, causing a glitch to occur on the pin during power

    up. To avoid this behavior, power the VDD pins before or with the VDDIO pins, ensuring that the VDD pins

    have reached 0.7 V before the VDDIO pins reach 0.7 V.

    "

     

    Regards,
    Cody

  • 0 in reply to Cody Watkins
    Intellectual 270 points

    Cody-san,

    Thank you for having you confirm it.
    I confirm a data sheet again.

    Best Regards,
    Koichi