Serial Connection

The ROM serial bootloader of Espressif chips uses a 3.3V UART serial connection. Many development boards make the serial connections for you onboard.

However, if you are wiring the chip yourself to a USB/Serial adapter or similar then the following connections must be made:

ESP Chip Pin	Serial Port Pin
TX	RX (receive)
RX	TX (transmit)
Ground	Ground

Note that TX (transmit) on the ESP chip is connected to RX (receive) on the serial port connection, and vice versa.

Do not connect the chip to 5V TTL serial adapters, and especially not to “standard” RS-232 adapters! 3.3V serial only!

Serial Port Settings

When communicating with the ESP32 ROM serial bootloader, the following serial port settings are recommended:

Baud rate	115200
Data bits	8
Stop bits	1
Parity	None
Flow control	None