ESP8266 Community Forum

- Sun Jul 01, 2018 4:16 pm #76772 Microcontrollers typically have a pull-up resistance between 50K and 100K. This is considered weak. It is okay for keeping unconnected pins at a stable logic level. They are also useful to pull up some local circuits but this needs to be evaluated on a case by case basis.

The ESP8266 has poor documentation and I didn't expect to find the specification for it. The ESP32 has a specified pull-up/down resistance of 45K.

A strong pull-up is relative thing. I often will use 1K or less when I need a strong pull-up. Like if there will be a lengthy cable run or to a higher current switch contacts. I have used 12 volts as the pull up voltage with a 470 Ohm resistor for pull-up. (with a high value series current limiting resistance at the port pin)

- Mon Jul 02, 2018 9:44 am #76793 Hi, I checked again, with another brand new ESP8266-12F, this time using following manual programming procedure: at power up tie GPIO0 to GND, then remove GND connection (release to floating state), and download program. Then restart with GPIO0 connected with 3k3 (instead of 10k) to +3.3V. The output remains low!

So no oscillations, (as I had with a 10k pullup), but no reaction at all.

Conclusion:

1. 10k pullup causes oscillations when output is supposed to be low

2. 3.3k pullup does not change the output state to anything but low

I am lost now.

It is never too late to learn

- Mon Jul 02, 2018 11:18 am #76796 If you look at the attachment I posted (which doesn't have reset wiring), it shows usage of all pins (including GPIO 0) as output. In the case of GPIO 0 it is used as a current sink - I have some notes knocking about and I know that some of the pins can only be used certain 'ways round'. Perhaps GPIO 0 needs setup like that. I will see if I can find the old notes.

FullEvalBoard.pdf

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- Mon Jul 02, 2018 11:25 am #76797 Found it : I wrote this as a note to myself 2 years ago :

GPIO 0 i/o : can be used as an input, however it is also used for flash selection on power up (0v = flash), and is driven high by default on the internal circuitary. pinMode(INPUT), dont use INPUT_PULLUP. Because of boot/flash reqs of internal circuitary, an output must be driven by setting LOW, and the external device must be connected between GPIO0 and +Vcc.

### HOWEVER: I have tried using it as CE o/p pin for 5110 LCD and it works fine, no special wiring!