Strapping Pins And Other Special Pins - Espressif Systems ESP32 Design Manuallines

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1.3.5. Strapping Pins and Other Special Pins

GPIO0 is one of the strapping pins, and its level state in the power-on reset process is
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related to download:
- "1": enter Flash startup mode, and the chip defaults to "1".
- "0": enter download mode.
Meanwhile, GPIO0 can also connect to other chips, such as MCLK (master clock), so using
GPIO0 for other functions is not recommended.
GPIO2 is another strapping pin, and its level state in the power-on reset process is also
•
related to download:
- "0": enter download mode, and the chip defaults to "0".
Meanwhile, GPIO2 can be used for connection to SDIO/MMC (for example, SD card), so
using GPIO2 for other purposes is not recommended.
�� Note:
In your design, it is recommended to reserve test points for GPIO0 and GPIO2, or to connect a button for
downloading.
For example:
Espressif
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Figure 1-7. Reference Circuit for USB-UART Chip
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1. Schematic Design
2019.01