Datasheet

2. Pin Definitions
• MTDI
• GPIO0
• GPIO2
• MTDO
• GPIO5
Software can read the values of these five bits from register ”GPIO_STRAPPING”.
During the chip’s system reset release (power-on-reset, RTC watchdog reset and brownout reset), the latches
of the strapping pins sample the voltage level as strapping bits of ”0” or ”1”, and hold these bits until the chip
is powered down or shut down. The strapping bits configure the device’s boot mode, the operating voltage of
VDD_SDIO and other initial system settings.
Each strapping pin is connected to its internal pull-up/pull-down during the chip reset. Consequently, if a strapping
pin is unconnected or the connected external circuit is high-impedance, the internal weak pull-up/pull-down will
determine the default input level of the strapping pins.
To change the strapping bit values, users can apply the external pull-down/pull-up resistances, or use the host
MCU’s GPIOs to control the voltage level of these pins when powering on ESP32.
After reset release, the strapping pins work as normal-function pins.
Refer to Table 3 for a detailed boot-mode configuration by strapping pins.
Table 3: Strapping Pins
Voltage of Internal LDO (VDD_SDIO)
Pin Default 3.3 V 1.8 V
MTDI Pull-down 0 1
Booting Mode
Pin Default SPI Boot Download Boot
GPIO0 Pull-up 1 0
GPIO2 Pull-down Don’t-care 0
Enabling/Disabling Debugging Log Print over U0TXD During Booting
Pin Default U0TXD Active U0TXD Silent
MTDO Pull-up 1 0
Timing of SDIO Slave
Pin Default
Falling-edge Sampling
Falling-edge Output
Falling-edge Sampling
Rising-edge Output
Rising-edge Sampling
Falling-edge Output
Rising-edge Sampling
Rising-edge Output
MTDO Pull-up 0 0 1 1
GPIO5 Pull-up 0 1 0 1
Note:
• Firmware can configure register bits to change the settings of ”Voltage of Internal LDO (VDD_SDIO)” and ”Timing
of SDIO Slave” after booting.
• The module integrates a 3.3 V SPI flash, so the pin MTDI cannot be set to 1 when the module is powered up.
The strapping pins need a setup and hold time before and after the EN signal goes high. For details please refer
to Section Strapping Pins in ESP32 Datasheet.
Espressif Systems 5 ESP32-WROOM-32 Datasheet V2.9