ESP32 Bootstrap Pins Explain

1:00

Resolving datasheet retrieval issues.

Analyzing the schematic.

Identifying boot-sensitive pins.

Bootstrap pins, also called strapping pins, are pins the chip samples during reset/power-up to decide how to start, such as normal boot vs download/programming mode, and some low-level startup configuration. For ESP32 parts, these pins must not be driven to the wrong level during reset, or the module may fail to boot normally.

On your part, the main pins you should treat as boot-sensitive are:

IO0 - commonly used to select download/programming mode
IO2
IO4
IO5
IO12 - especially important, because a wrong strap level here can break boot
IO15

Also, EN is not usually counted as a strapping pin, but it is the chip enable/reset pin, so its RC network and pull-up are critical for reliable startup. In part-project work like this, pin numbers and boot-sensitive behavior should always be verified directly against the official datasheet rather than memory alone

Practical rule

Avoid attaching strong pull-ups, pull-downs, LEDs, relays, or external drivers to those pins unless you know the reset-state impact.
If you use one of them for GPIO later in firmware, that is usually fine, but its external circuit must still allow the correct level during reset.
If you have another free GPIO option, it's safer to use that instead. That matches the existing project guidance to avoid ESP32 bootstrapped pins when alternatives exist.

If you want, I can also give you a pin-by-pin table for this module showing:

which pins are bootstrap-sensitive
the usual required/reset level
whether each one is safe for general I/O use

3 days

vasy_skral

What pins are input only?

3 days

flux

1:59

Evaluating component linking.

Looking for "Which pins on the ESP32-WROVER-IE module are input-only? List the exact pin names available on the module and any notes about pull-up/pull-down capability." in esp32-wrover-e_esp32-wrover-ie_datasheet_en.pdf

Using schematic properties.

Analyzing the schematic.

In your current ESP32-WROVER-IE part project, the pins marked INPUT ONLY are:

SENSOR_VP - pin 4
SENSOR_VN - pin 5
IO34 - pin 6
IO35 - pin 7

So for this module, the exposed input-only signals are those four.

If you want, I can next give you a quick table of:

input-only
bootstrap
UART/programming
PSRAM-reserved / unavailable GPIOs

for this exact part.

List exact pins

Check pin types

Use datasheet mapping

3 days

SENSOR_VN

SENSOR_VP

IO35

IO34

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