Espressif Systems ESP Faq page 172

Chapter 5. Hardware related
5.3 Hardware design
5.3.1 The I2S pins of ESP32 are scattered. Can I route I2S signals to adjacent pins?
For example, to GPIO5, GPIO18, GPIO23, GPIO19, and GPIO22, or to
GPIO25, GPIO26, GPIO32, and GPIO33.
• All I2S signals can be routed to different I/Os freely. Please note that some I/Os can only be set as input. For
details, please refer to Section Peripheral Pin Configurations and Appendix IO_MUX in the
5.3.2 How can I stop the power loss of VDD3P3_RTC after ESP32 enters Light-sleep
mode?
After entering Light-sleep mode, if RTC power loss occurs, the level of the GPIO corresponding to the
VDD3P3_RTC pin will be pulled low, causing external RTC or other devices to malfunction. There are
two possible ways to solve this problem:
• Set the RTC hardware voltage control register (RTC_CNTL_REG) to control the voltage. Specif-
ically, set the FORCE_PU and FORCE_PD bits in the RTC_CNTL_REG register to 1, namely,
RTC_CNTL_REG |= RTC_CNTL_FORCE_PU_M | RTC_CNTL_FORCE_PD_M;.
• Set GPIO hold pins. The ESP32's Light-sleep mode supports GPIO hold function, which can set
some GPIO pins as hold pins to maintain their voltage level when the system enters Low-power
mode. Specifically, the VDD3P3_RTC pin can be set as a hold pin to maintain its voltage. The
relevant code snippet is as follows:
esp_sleep_pd_config(ESP_PD_DOMAIN_RTC_PERIPH, ESP_PD_OPTION_ON);
esp_sleep_enable_gpio_wakeup();
gpio_hold_en(GPIO_NUM_X);
Among them, ESP_PD_DOMAIN_RTC_PERIPH represents the power domain of the RTC subsys-
tem. ESP_PD_OPTION_ON enables the power domain. And the gpio_hold_en() function can set the
specified GPIO pin as a hold pin. After setting the VDD3P3_RTC pin as a hold pin, even if the system
enters Light-sleep mode, the voltage of the pin will be held.
Please note that using the GPIO hold function will increase the power consumption of the system, so the
appropriate solution should be selected according to the specific application scenario. If only the power
supply of the RTC hardware needs to be held, the first method can be adopted. If the power supply of
other external devices needs to be held as well, the second method can be adopted.
5.3.3 What should be noted when I configure the pins of ESP32?
• You may assign most of the digital peripherals to any pins through GPIO Matrix. However, func-
tions such as SDIO, high speed SPI, and analog can only be realized via IO MUX.
• For details, please refer to
Note:
• Strapping pins have default levels. Please refer to
• GPIO34 ~ GPIO39 can only be set as input without software-enabled pull-up or pull-down func-
tions.
Espressif Systems
GPIO & RTC GPIO.
ESP32
155
Submit Document Feedback
Datasheet.
ESP32 Datasheet.
Release master