[sdiy] Arduino schem - diode in series with R at reset pin?

[Ove Ridé]

That diode is likely there specifically due to the capacitor used on
the serial DTR line to send a reset pulse. The purpose of that is that
when DTR goes from high to low, the capacitor is charged through the
10k pullup resistor, as the reset line slowly returns to +5V over a
couple of milliseconds perhaps. But when DTR goes high and the
capacitor is charged, the reset line suddenly sees 10V until the 5V
charge in the capacitor is depleted. The diode acts as a short to +5V
to allow the charge to quickly be disposed of.

However, the diode is missing on most Arduino schematics, and it's
likely they decided that it wasn't needed due to the AVR chip's
excellent internal clamp diodes.

On 23 April 2015 at 16:27, Justin Owen <juzowen at gmail.com> wrote:
> Hello,
>
> http://i.stack.imgur.com/cPCB4.png
>
> Some of the Arduino schematics have a diode in parallel with the normal R to VRef on the Reset Pin (Pin 1 in the above link).
>
> Can anyone explain what the diode is doing and why it only seems to be on Arduino schems?
>
> FYI, I'm looking specifically at using the Atmega 328P in a non-Arduino, stand-alone circuit.
>
> Thanks,
>
> - Justin
>
>
>
>
>
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-- 
/Ove

Blog: <http://blog.gg8.se/>

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