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