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GPIO states rtc only mode

Nicolas Deup
Intellectual 590 points

Dear all,

What may be the GPIO output state of the C5535 when toggling from Run to RTC Only mode and vice versa ?

If GPIO was in output configuration at high (low) level in RUN mode, will it be in High-Z once DSP configured in RTC only mode and keep previous high state (low) level back in RUN mode ? And what about timing ?

Thanks.

Nicolas

  • 0
    TI__Mastermind 30110 points

    Hi Nicolas,

    During RTC-only mode the CVDD core power is off (DSP_LDO is off) so the bus holders will weakly pull the GPIO to its previous state. However, the bus holders can be driven the opposite direction with enough current like a short - this prevents excessive current draw and device damage. See 4.8.2 Bus Holders and the end of Table 5.3 in http://www.ti.com/lit/ds/symlink/tms320c5535.pdf

    Exiting from RTC-only requires booting the DSP. Depending on the GPIO and chosen boot source, the state may change during the bootloader and when it changes the EBSR pin mux register. After boot, your program can reassert the output. Bootloader times vary from milliseconds to seconds.

    You could write to the register at the beginning of the bootloader with -reg_config argument to the hex55 boot image creation tool. See http://www.ti.com/lit/an/sprabl7b/sprabl7b.pdf

    Hope this helps,
    Mark