Use this forum to chat about hardware specific topics for the ESP8266 (peripherals, memory, clocks, JTAG, programming)

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By mlefevre
#77805 I realize that this thread is over 3 years old but I came across it because I'm having the same problem. GPIO 0 wants to sit at 1.9v despite the pullup and the chip won't enter flash mode as a result. I'm hoping one of the original posters found the problem and can share. Could it just be defective ESP-12e modules. Both of the ones I have do this.
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By mlefevre
#77952 I figured out my problem. In my original design, I was not using GPIO15 and pulled it down with a 10K resistor. Later, during development, I needed another GPIO and I decided to use GPIO15 and I connected it to an existing circuit that employed a 100K pulldown resistor. I found that when GPIO15 is pulled down with only 100K, GPIO0 does not rise to 3.3v even with a 10K pullup resistor. If you change the pulldown resistor to 10K, GPIO0 rises to 3.3v. I don't know what happens on GPIO15 during boot but 100K is too large a pulldown resistor for it to work properly.