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Prop2 Eval Boards all need a mod to fix SD/Flash brownouts — Parallax Forums

Prop2 Eval Boards all need a mod to fix SD/Flash brownouts

evanhevanh Posts: 15,405
edited 2023-09-08 14:01 in Accessories

The reset circuit of the Eval Boards feed into the enable of the "Common VIO" voltage regulator. This has the unfortunate side effect of, when triggered by comport DTR toggle, a brief shutdown of supply to the Flash EEPROM and, if present, the SD card. The supply capacitor droops to about 1.5 volts before being regulated again.

I'm recommending the removal of R802 and fitting of R801 as the fix.

Here's a scope screenshot of a DTR toggle at beginning of program download:
Blue trace is pin P60, with SD card pull-up, so represents the supply to the SD card.
Pink trace is VIO volts V5663.
Orange trace is P2_RESN.


  • Not sure here, but I remember @VonSzarvas saying that there was a intend behind that to reset SD by holding reset down manually for a longer amount of time.

    Might be I misunderstood, happens a lot lately.


  • evanhevanh Posts: 15,405
    edited 2023-09-12 03:54

    You are correct, but the flaw is much worse than the benefit. Adjusting the timing values to make the brownout a proper power down would probably provide both but I figured that since the EC/EC32MB cards don't do any of this then we may as well make the Eval boards the same.

    Ideally, software should be doing the SD power cycling anyway. That's been learnt the hard way now too.

    On that note: Roger has done a good job of his add-on board. It's a suitable upgrade providing 4-bit capable interface as well -
    I've been pottering away at it from time to time. One day FlexProp will fully support it. :)

  • evanhevanh Posts: 15,405
    edited 2024-05-11 13:36

    SD specs says an official power down of an SD card is taking the supply below 0.5 volts for 1.0 ms or more.

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