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Original question:

TMS320F28P650DK: State of I/O During Boot-Up

TMS320F28P650DK: State of IO Before Configuration

Mike Allette
Intellectual 365 points

Part Number: TMS320F28P650DK

Hi,

 

How do I confirm the state of the IO when the MCU starts up, before the MCU is configured?

Trying to bring up a board with the TMS320F28P650DK and trying to find out what is running in the MCU before it is actually configured.

  • 0
    TI__Genius 9970 points

    Hi Mike,

    On F28P65x, all GPIOs come up as inputs on reset, and the internal pullups are disabled (except for GPIOs that are not bonded out), so the I/Os are effectively high-impedance until your software reconfigures them.

    For “what is running before it is actually configured”: once XRS is released, the device executes Boot ROM first (bootloader), then it proceeds based on the selected boot mode (boot to Flash entry point, wait boot, .....).

    To confirm the I/O state right at startup, in CCS, halt at reset and read the GPIO registers (DIR/MUX/PUD) to verify they’re still at defaults before your init code runs.

    If you want a guaranteed known external level during boot, use external pull-ups/downs on the specific pins (don’t rely on internal pulls during early boot), or keep downstream circuitry disabled until your firmware asserts an enable.

    Best Regards,

    Masoud

  • 0 in reply to Masoud Farhadi
    Intellectual 365 points

    Hi Masoud,

    I have a board that I designed with the F28P65x part and am having an issue applying the 3.3V VDD/VDDIO power to it without the F28P65x pulling a lot of current and tripping my power supply. I may or may not have something connected incorrectly. I have a reset button that holds XRS low when pressed. If i hold that low, when applying power, there should be nothing happening on the chip right? Instead my power supply trips due to a bunch of current being pulled.

    Is there a default boot mode the the device goes to on initial power up before it is even connected to something like a XDS110 Debug probe? When the board is fresh out the fab house?

    What decides it's initial boot mode or default boot mode?

  • 0 in reply to Mike Allette
    TI__Genius 9970 points

    Hi Mike,

    If your supply is tripping while XRS is held low, that’s pointing to a hardware issue. I would look for common culprits like solder bridge and incorrect orientation.

    Also, if a connected circuit is forcing a pin beyond rails, you can still get injection current.

    On the boot mode question, for the F28P65x LaunchPad, the boot select pins are GPIO72 and GPIO84, and with both HIGH the device boots from Flash by default.

    Best Regards,

    Masoud

  • 0 in reply to Masoud Farhadi
    TI__Genius 9970 points

    One more thing to check is VDD supply configuration. Say if you're enabling internal VREG while also forcing external power, it will cause conflicts.

    Best Regards,

    Masoud 

  • 0 in reply to Masoud Farhadi
    Intellectual 365 points

    I ran an Xray to check for solder bridges and checked the orientation and those checked out.

    I have VREGENZ tied to GND.

    I don't have GPIO72 and GPIO84 connected to anything on my board. What issues can arise if i cant set those pins to a known state at initial start up?

  • +1 in reply to Mike Allette
    TI__Genius 9970 points

    If those pins are left floating, their logic level at that sampling instant can be random based on the environment noise. But floating boot pins won’t cause a power issue like a supply trip. That’s more likely from a short or something in the power circuit. So you’ll want to fix both, but they’re separate issues.

    Best Regards,

    Masoud