- Sat Aug 15, 2015 4:24 pm
#26100
Hi, the ESP8266 is a tricky little beast. Some of the pins have different uses depending on the mode the ESP or at boot.
GPIO 2 needs the resistor as:
It needs to be floating or pulled high at boot (still being debated) but not low.
it is also connected to UART Tx & the blue led). Only impotant during flashing when in run mode it can be used as a normal GPIO.
It gets a bit complicated with the ESP8266-01, other formats with more GPIOs broken out you would just not use GPIO 2, we don't have much choice.
We have 3 modes that the ESP can be in:
Boot mode - lasts about 250ms - GPIO 2 is an input & can be high or floating (there are different opinions about this) but not low.
Flash mode - follows boot mode & lasts until flash completed or power cycled - GPIO 2 is UART Tx with a blue indication led - can be high, floating or low, as long as connected by a high impedance, such that can be overcome by other devices using that line. 1K to 10K generaly seem to work. The blue led not functioning as expected gives an indication that the impedance is to low.
Run mode - follows boot mode & or flash mode - GPIO 2 only now functions as a GPIO.
In some applications it may be possable contend with all three modes, others my require that the ESP be removed from its application to be flashed. I have one for opening some gates that uses both GPIO 0 & 2, with the parts I had available it was possable to contend with boot & run mode, but there was no way I could get the impedance low enough to to be able to flash aswell. I dont consider this a problem, should the ESP need to be reflashed it will be unplugged & flashed on a different board.
Blue led:
Boot mode - flashes at power up to indicate which mode is to be entered. Once for flash mode, twice for run mode & others that you shouldn't come across during this.
Flash mode - flashes to indicate UART Tx trafic.
Run mode - TBH I can't remember what if anything it does - will update.
If the led does not opperate as expected it is an indication that the connection to GPIO 2 is having an effect. This may or may not be a problem depending on the mode you are in.
There are other modes, SD card boot is the only other hardware selectable mode that I know of. Others are set via code after boot.
Hope that helps & gives you an indication of why even a slight change can make a difference.
GPIO 2 needs the resistor as:
It needs to be floating or pulled high at boot (still being debated) but not low.
it is also connected to UART Tx & the blue led). Only impotant during flashing when in run mode it can be used as a normal GPIO.
It gets a bit complicated with the ESP8266-01, other formats with more GPIOs broken out you would just not use GPIO 2, we don't have much choice.
We have 3 modes that the ESP can be in:
Boot mode - lasts about 250ms - GPIO 2 is an input & can be high or floating (there are different opinions about this) but not low.
Flash mode - follows boot mode & lasts until flash completed or power cycled - GPIO 2 is UART Tx with a blue indication led - can be high, floating or low, as long as connected by a high impedance, such that can be overcome by other devices using that line. 1K to 10K generaly seem to work. The blue led not functioning as expected gives an indication that the impedance is to low.
Run mode - follows boot mode & or flash mode - GPIO 2 only now functions as a GPIO.
In some applications it may be possable contend with all three modes, others my require that the ESP be removed from its application to be flashed. I have one for opening some gates that uses both GPIO 0 & 2, with the parts I had available it was possable to contend with boot & run mode, but there was no way I could get the impedance low enough to to be able to flash aswell. I dont consider this a problem, should the ESP need to be reflashed it will be unplugged & flashed on a different board.
Blue led:
Boot mode - flashes at power up to indicate which mode is to be entered. Once for flash mode, twice for run mode & others that you shouldn't come across during this.
Flash mode - flashes to indicate UART Tx trafic.
Run mode - TBH I can't remember what if anything it does - will update.
If the led does not opperate as expected it is an indication that the connection to GPIO 2 is having an effect. This may or may not be a problem depending on the mode you are in.
There are other modes, SD card boot is the only other hardware selectable mode that I know of. Others are set via code after boot.
Hope that helps & gives you an indication of why even a slight change can make a difference.
