ESP32 datasheet(32/64 Pages) ESPRESSIF

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4. Peripherals and Sensors

4.1 Descriptions of Peripherals and Sensors

4.1.1 General Purpose Input / Output Interface (GPIO)

ESP32 has 34 GPIO pins which can be assigned various functions by programming the appropriate registers.

There are several kinds of GPIOs: digital-only, analog-enabled, capacitive-touch-enabled, etc. Analog-enabled

GPIOs and Capacitive-touch-enabled GPIOs can be configured as digital GPIOs.

Most of the digital GPIOs can be configured as internal pull-up or pull-down, or set to high impedance. When

configured as an input, the input value can be read through the register. The input can also be set to edge-trigger

or level-trigger to generate CPU interrupts. Most of the digital IO pins are bi-directional, non-inverting and tristate,

including input and output buffers with tristate control. These pins can be multiplexed with other functions, such as

the SDIO, UART, SPI, etc. (More details can be found in the Appendix, Table IO_MUX.) For low-power operations,

the GPIOs can be set to hold their states.

4.1.2 Analog-to-Digital Converter (ADC)

ESP32 integrates 12-bit SAR ADCs and supports measurements on 18 channels (analog-enabled pins). The ULP-

coprocessor in ESP32 is also designed to measure voltage, while operating in the sleep mode, which enables

low-power consumption. The CPU can be woken up by a threshold setting and/or via other triggers.

With appropriate settings, the ADCs can be configured to measure voltage on 18 pins maximum.

Table 7 describes the ADC characteristics.

Table 7: ADC Characteristics

Parameter

Description

Min

Max

Unit

DNL (Differential nonlinearity)

RTC controller; ADC connected to an

–7

LSB

external 100 nF capacitor; DC signal input;

INL (Integral nonlinearity)

ambient temperature at 25 °C;

–12

LSB

Wi-Fi&BT off

Sampling rate

RTC controller

200

ksps

DIG controller

Msps

Notes:

• When atten=3 and the measurement result is above 3000 (voltage at approx. 2450 mV), the ADC accuracy

will be worse than described in the table above.

• To get better DNL results, users can take multiple sampling tests with a filter, or calculate the average value.

• The input voltage range of GPIO pins within VDD3P3_RTC domain should strictly follow the DC characteristics

provided in Table 13. Otherwise, measurement errors may be introduced, and chip performance may be

affected.

By default, there are ±6% differences in measured results between chips. ESP-IDF provides couple of calibration

methods for ADC1. Results after calibration using eFuse Vref value are shown in Table 8. For higher accuracy,

users may apply other calibration methods provided in ESP-IDF, or implement their own.

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