Intro

So, you definitely know, that you can optionally enable or disable weak (because resistance is pretty high) pull-up (for positive) or pull-down (for negative) internal resistor to set stable logic level.

But what is the actual resistance have those pull-up/pull-down resistors? Let's find out this 🤨

Code

Using Arduino framework I configured GPIO1 pin as OPEN DRAIN with pull-up:

#define GPIO_PULLUP 1
 
// the setup function runs once when you press reset or power the board
void setup() {
  // initialize digital pin LED_BUILTIN as an output.
  pinMode(GPIO_PULLUP, INPUT_PULLUP);
 
  pinMode(LED_BUILTIN, OUTPUT);
 
 
}
 
// the loop function runs over and over again forever
void loop() {
  digitalWrite(LED_BUILTIN, HIGH);  // turn the LED on (HIGH is the voltage level)
  delay(1000);                      // wait for a second
  digitalWrite(LED_BUILTIN, LOW);   // turn the LED off by making the voltage LOW
  delay(1000);                      // wait for a second
}
 

Pin States

So, after configuring GPIO1 now can have one of two states:

SINK LOW (GPIO: 0V)	WEAK HIGH (GPIO: 3.3V)

 

Measuring

It's easy to do measuring by using multimeter with uA regime, so I just connect positive probe to the GPIO1 and negative probe to the devboard GND.

And this cause current flow through internal pull-up resistor, so we can see the real value:

Calculations

Because MCU powering voltage is 3.3V (measured before) and the current is 73.4uA, the resistance is:

Datasheet (Update from 2024/02/03)

Hah, I just found that resistance is openly written in the ESP32-S3 datasheet, and as you can see value 45kOhm is corresponds to the calculated resistance 44.96kOhm:

Pull in deep-sleep (Update from 2026/03/03)

Looks like internal pull-up will work in deep-sleep (e.g. for buttons).

Conclusions

• Earlier I expected weak internal resistors value ~47k, so the reality confirmed it 😎
• Calculated value corresponds to the specified in the datasheet