Notes - Espressif Systems ESP32 Series Manual

4.1 ESP-WROOM-32 Module
NO Name
32 NC
33 IO21
34 RXD0
35 TXD0
36 IO22
37 IO23
38 GND

4.1.3 Notes

• The module uses one single pin as the power supply pin. The user can connect the module to a 3.3V power
supply. The 3.3V power supply works both for the analog circuit and the digital circuit.
• The EN pin is used for enabling the Wi-Fi functionality. Set the EN pin high for normal working mode.
• The SMD Module features two working modes: the UART Download mode and the Flash Boot mode. In
the UART Download mode, firmware can be downloaded into the flash memory or the internal memory by
configuring the flash download tool. If the firmware is burnt into the internal memory, it can only run this time
when the module is powered on. Once the module is powered down, the internal memory will clear up.
However, if the firmware is burnt into the flash, it will be stored and can be recalled at any time.
• Lead the GND RXD TXD pins out and connect them to a USB-to-TTL tool for firmware download, log-printing
and communication.
By default the initial firmware has already been downloaded in the flash. If users need to re-download the firmware,
they should follow the steps below:
1. Set the module to UART Download mode.
2. Pull IO0 and IO2 low.
3. Power on the module and check through the serial if the UART Download mode is enabled.
4. Download the firmware to flash using the ESP Flash Download Tool.
5. After downloading, keep IO15 low and pull IO0 high to enable the SPI Boot mode.
6. Power on the module again. The chip will read and execute the firmware during initialization.
Notice:
• During the whole process, users can check the status of the chip with the log printed through UART. If
the firmware cannot be downloaded or executed, users can check if the working mode is normal during
the chip initialization by looking at the log.
• The serial tool cannot be opened for both the log-print and flash-download tools simultaneously.
• Please download the ESP Flash Download Tool from Espressif's website:
Espressif Systems
Function
-
GPIO21, VSPIHD, EMAC_TX_EN
GPIO3, U0RXD, CLK_OUT2
GPIO1, U0TXD, CLK_OUT3, EMAC_RXD2
GPIO22, VSPIWP, U0RTS, EMAC_TXD1
GPIO23, VSPID, HS1_STROBE
GND
25
4 HARDWARE DEVELOPMENT
Flash Download
ESP32 Hardware Design Guideline V1.0
Tool.