Re: GPIOs as input pins during boot process
Posted: Sat Nov 15, 2014 12:56 pm
You still have another choice: having a GPIO high or low during bootstrap for choosing the correct operating mode doesn't mean that you have to TIE the GPIO directly to either VCC or GND: you can connect it through a pull-up or pull-down resistor that is tied to VCC/GND,
If it has a high enough (~47 kohms is a good choice), then you can later on use the GPIO as input and drive it high or low depending upon your needs: when not driven, the resistor will drive the input to the default bootstrap level, but if you force it to the other level, it will allow you to do so, absorbing the voltage difference by conducting with a current I = V / R. As R is high, the resulting current is low, despite the large voltage difference, but it is not a short between a high and low voltage level, which would blow some fuses somewhere because of the high uncontrolled inrush current when R is very low...
However, this only works if the attached device that you want to connect to your input has the correct default level to allow bootstrapping the ESP8266 in the right mode.
If it has a high enough (~47 kohms is a good choice), then you can later on use the GPIO as input and drive it high or low depending upon your needs: when not driven, the resistor will drive the input to the default bootstrap level, but if you force it to the other level, it will allow you to do so, absorbing the voltage difference by conducting with a current I = V / R. As R is high, the resulting current is low, despite the large voltage difference, but it is not a short between a high and low voltage level, which would blow some fuses somewhere because of the high uncontrolled inrush current when R is very low...
However, this only works if the attached device that you want to connect to your input has the correct default level to allow bootstrapping the ESP8266 in the right mode.