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SM320F28335-EP: GPIO Initialization Delay

Dragos Moscalu
Prodigy 170 points

Part Number: SM320F28335-EP
Other Parts Discussed in Thread: TMS320F28335

Hello TI technical team,

After releasing the XRS line to High logic, the microcontroller boots the first Software sequences, while I assume all GPIOs will be initialized as Hi-Z, until SW defines the proper state for them.

Quiestion1: Does all GPIOs have both Pull-Up and Pull-Down enabling possibility?
Quiestion2: How long it takes to have the proper pull-up/down SW settings in place after XRS was released?
Quiestion3: Can we avoid an uncontrolled High Level during GPIO80 initialization?
Quiestion4: Are there any differences, related to GPIO initialization, compared to TMS320F28335

We are investigating the GPIO80 initialization sequence, that is responsible for an external RESET(active high) for another device. With no external Pull-Up/Down resistors, we observed, a logic HIGH level, for about ~35ms.

Before adding an External Pull-Down resistor, I would like to understand the impact with the internal active Pull-Up/Down circuits, during the start-up sequence.

Thank You for your support!

  • 0
    TI__Mastermind 42195 points

    Dragos,

    1. Externally a pull-up or pull-down can be added. Internally only a pull up is available, and cannot be configured. Please see the default state of GPxPUD for the default state of the internal pull behavior.
    2. This entirely depends on the code being executed on the CPU, recommend that you characterize your code. If you are connecting to circuits that need a specific condition at startup please use external pull-resistors, it will take some time for BootROM to run and the device SW to configure the pins.
    3. yes, recommend external pull-down resistor for all pins that need a known state during startup.
    4. no, none that I am aware of.

    The internal pull up circuitry is not enabled on every pin by default, perhaps choosing one of those would be better for your application. An external pull-up is recommended for all pins that need a known state. Finally it sounds like this is an important reset circuit, I would recommend you think about what state you want the reset circuit to fail into. remember if the C2000 fails into a high-z state then the reset of the other device would be preserved by an external pull resistor, this may or may not be desirable. 

    Regards,
    Cody