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 ESP8266 ROM serial bootloader, the following serial port settings are recommended:

Baud rate

74880

Data bits

8

Stop bits

1

Parity

None

Flow control

None

Note

Baud rate 74880 is what the ESP8266 bootloader uses. The apps on top of the Espressif SDK (e.g. Arduino sketch) talk at 115200 if not specified otherwise.