Espressif Systems ESP Faq page 180

Chapter 5. Hardware related
5.3.41 When connecting an external flash to ESP32-WROOM-32D module, is it possible
if I do not use GPIO6 ~ GPIO11 pins?
• ESP32 has 3 sets of SPIs (SPI, HSPI and VSPI), which can access the external flash through the
SPI0/1(HSPI/VSPI) bus. The external flash connected to other pins (pins other than GPIO6 ~ GPIO11) can
only receive data for storage, but not run code. If you need to run code from flash, please connect the flash to
GPIO6 ~ GPIO11 pins only.
5.3.42 Do I need to add a shielding case to the PCB of ESP32 modules?
• Whether a shield needs to be added depends on the specific application scenarios and requirements.
• In some high-demand application scenarios, such as environments with severe wireless communication in-
terference or high electromagnetic compatibility (EMC) testing requirements, adding a shield can effectively
reduce external interference and mutual interference on the PCB board, improving system stability and relia-
bility. At this time, the shield should be made of conductive material and grounded to ensure its effectiveness.
• On the other hand, if the application scenario is relatively simple, such as low wireless communication inter-
ference and low EMC requirements, the effect of adding a shield may not be very obvious and may increase
system cost and complexity.
• If the board has other signal interference, such as 2G, 3G, 4G, Wi-Fi, Bluetooth, Zigbee, etc., it is recom-
mended to add a shielding case.
5.3.43 Do I must use GPIO0, GPIO1, or GPIO3 of ESP32 as the I2S CLK pin?
• The MCLK pin must use GPIO0, GPIO1, or GPIO3. The other clock pins can use any GPIOs. Note that
GPIO0 is generally not recommended for other functions because it is a strapping pin.
5.3.44 Does the ESP32-U4WDH chip support external PSRAM chips?
• The ESP32-U4WDH chip supports external PSRAM chips. However, only the
leased by Espressif is supported. Third-party PSRAM chips are not supported.
• For hardware design, all the PSRAM pins except for the CS pin can be multiplexed with Flash. For more
information, please refer to the
• Also, when designing the PCB, please make sure that the GND of the PSRAM to the GND of the ESP32-
U4WDH is as short as possible; Otherwise, the signal quality may be affected.
5.3.45 Does ESP32 support connection to an external SD NAND flash chip (instead of
the default NOR flash chip) via the SPI0/SPI1 interface for storing application
firmware?
• The ESP32 chip does not support external SD NAND Flash chips using the SPI0/SPI1 (connect the core Flash)
interface.
• If you want to store external data, it is recommended to use the SPI2, SPI3, or SDIO interface of ESP32 to
connect to an external NAND SD chip.
• SPI2 and SPI3 can be used via any GPIOs, while the SDIO interface can only be used via the specified interface.
For more information, please refer to Section Peripheral Pin Configurations in the
Espressif Systems
ESP32 Hardware Design Guidelines.
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