Re: Inverting RST pin (using configuration file) not working on Raspberry Pi?

[Martin Stejskal]

Hi,

 basically Konrad provided scheme which I had in my mind and well explained :)

Just one more thing about using 3.3V instead of 5V - you might have problems with limited crystal frequency. Then you might need to reduce internal clock settings and also reduce programming bitrate.

Roger, I agree that they should "survive" more, but as you correctly mentioned, that current will sum, so it is better to keep it low.

 Martin S.

On Wed, 2 Jun 2021 at 00:04, Rogier Wolff <R.E.Wolff@bitwizard.nl> wrote:

On Tue, Jun 01, 2021 at 09:56:13PM +0200, Martin Stejskal wrote:
> Thing is that every GPIO suppose to have some
> protection diode (in generic - "every" IC - there are exceptions of
> course). They typically stand like ~1 mA without problems.

That diode is quite beefy! In general ("Typical") it can take about
10mA!

That doesn't mean that it is safe to do so. Suppose you have two pins
doing that 10mA, then that 20mA will end up on the 3.3V rails. Now if
there is more than 20mA of power draw on the 3.3V, but if the 3.3V
stuff goes in power-save or something like that, you can easily
over-volt your 3.3V stuff. Really easy to mess up. So a safe margin,
say a factor of ten is reasonable.

Somehow, on the RPI, I suspect that the IO cells of the broadcom CPU
can be a bit less "beefy" than "typical". Another reason to keep a
safe margin.

        Roger.

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