bizarre wave on GPIO0

[wakky]

I observed bizarre wave on GPIO0 at the time of reset.
My circuit is most simile and use 3.3V DC.
What is the wave?

[wakky]

GPIO0 wave at download https://www.facebook.com/computerartisa ... 369391869/
and other man's report https://www.facebook.com/photo.php?fbid ... 912&type=3

[Espressif_Kelly]

Dear Wakky,

GPIO0 of ESP8266EX can output the clock frequency of the external cystal(e.g. 26Mhz or 40MHz) by default.

Please check it by measuring the frequency of this bizarre wave.

Any more questions, please let us know.

Thanks.

[wakky]

Dear Espressif_Kelly
Frequency is 27.5MHz
https://www.facebook.com/photo.php?fbid ... =3&theater

> GPIO0 of ESP8266EX can output the clock frequency of the external cystal
I understood.

Why is the voltage from -1V to 5V over this GPIO0?
This voltage from -1V to 5V gives damege to my circuit.

Wave at download time is https://www.facebook.com/computerartisa ... 369391869/

[wakky]

The bootloader have a bug -- set GPIO0 as clock output. Bootloader v1.2 and v1.4(b) have same bug.

[Espressif_Kelly]

Dear Wakky,

If you use 3.3V DC power supply, the peak to peak voltage of GPIO0 shoule be 3.3V.

Please double check if your oscilloscope has been correctly set.

Any more questions, please let us know.

Thanks.

[wakky]

Dear Espressif_Kelly
My friend observed that wave https://www.facebook.com/photo.php?fbid ... 912&type=3 .
Yellow wave is GPIO0's wave.
magenta wave is RESET's wave.

Yellow wave's behavior was as follows
(1)3.3V constant
(2)from -0.5V to 4.0V 26MHz wave.
(3)0.0V constant
(4)from -0.5V to 4.0V 26MHz wave.
(5)3.3V constant

I think that bootloader has bug.

[wakky]

My chip's photo
I have 5 chips, and all chip's GPIO0's behavior is same.

All my friend said "Your oscilloscope is broken". But they confirmed bizarre wave.

[wakky]

AT command firmware output same bizarre wave at reset.

[joostn]

Not sure why you're seeing the voltage go above 3.3 volt; probably parasitic capacitance and inductance is causing ringing close to the 27Mhz frequency.

Not the end of the world but I do think it is a bug because GPIO0 is also used as input during boot. Unfortunately it's baked in the boot ROM so we'll have to wait for the ESP32 to fix this

If the voltage overshoot causes problems you could add a resistor and a zener diode to clip it to 3.5 or so volts?