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Default state of ADC IOs on Piccolo TMS320F2806x processors?

Janet Stillman
Prodigy 90 points

For the pins that can be both ADC or GPIO, what are the disadvantages/advantages within the PIccolo of configuring the pins as GPIOs in output mode vs input with an external pulldown? (Not counting part count and PCB space). Does wiring as an ADC input and tying through 1 kO to ground improve ground bounce?

Is the power-on state of the ADC/GPIO pins that come up as GPIOs input, or output? Can the Piccolo be harmed if there's a long delay before the pins are reconfigured as outputs if there is no external pullup/pulldown?

Is the power-on and default state of the other GPIO pins input with a pullup? (I see the datasheet says by default they are configured with a pullup--just wanted confirmation that this meant input with a pullup or OD with a pullup rather than a driving output that drives high).

  • 0
    TI__Guru* 77460 points

    Janet,

    For those pins that can be either ADC or GPIO, the default config is that the IO function is turned off at reset.  This is because if the customer chooses to use as analog pins the voltage could be anything between 0 and 3.3V and giving a non- VIL/VOH compatible voltage to the input buffer could give un-needed leakage currents, etc.  Since they come up as analog feed thurs there should be no harm in changing them later in time(if at all) since any in range voltage is OK.

    When the IO function is enabled, they are configured as input such that the output buffer is off.  These AIOs do not have any internal PU, so if that node may not be driven an external pull would be desired.  Also in this mode the ADC path is still active(wired OR) if that is of any use(will not do any harm to the IO)

    For all other GPIOs your assertion, input with PU is correct except for the primary PWM pins; since for a FET this would turn it on at power up which is not wanted.  Those pins have the PU disabled at reset, but can be set by the user in SW if desired.  The TRM will show the default state of the PUD register for all other IOs.

    Best,

    Matthew