GPIO0 behavior on bootup


GPIO0 behavior on bootup

Postby rith87 » Wed Apr 27, 2016 8:23 pm

Hello folks,

I would like to use GPIO0 as an output. After looking around, I came across this image (from ... te-startup):


It seems like there is some ringing at 350Hz during startup and I managed to reproduce this on my ESP-12F. Is there any way to avoid this 350 Hz ringing? Also, can the folks at Espressif explain why this ringing occurs? Some kind of RF calibration?

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Joined: Mon Feb 02, 2015 4:52 pm

Re: GPIO0 behavior on bootup

Postby MarsTechH » Wed Apr 27, 2016 10:17 pm

1.You can try to use a low-pass filter, cutoff freq set around 1Hz or lower. If you dont think that's a good idea, use a simple RC circuit with a thansister to cut off those oscilitor when starting up(work likes a time-delay relay). Also... if you have extra GPIOs, use other GPIO to help : )

2. No idea, GPIO0 as a BOOT Mode selector, may trying to detecte? or... RF Calib, signaling something releated to crystal decting?

BTW, I'm not esp's folks : )

Posts: 140
Joined: Mon Oct 27, 2014 10:40 am

Re: GPIO0 behavior on bootup

Postby Espressif_Kelly » Fri Apr 29, 2016 3:16 pm


1.Wifi chip will have an internal reset in 30ms ~50ms after CHIP_EN has been pulled up.
2.And then GPIO0 will output the clock frequency (e.g 26MHz) of the external cystal by default.
3.After that, voltage of GPIO15, GPIO0 and GPIO2 will be sampled and ESP8266EX will choose the boot mode.
4.After flash boot, GPIO0 can be controlled by software.

More questions, please feel free to let us know.


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