Hardware Resources; Parameter Configuration; The Baud Rate - Espressif ESP8266 Technical Reference

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UART0 will default output some print while booting ,the baud rate of this period print
contents is relate with external crystal frequency.When using the 40M crystal,this section
print baud rate is 115200.When use the 26M crystal,this section print baud rate is 74880.
If this print affect application function, you can abandon print output indirectly while power-
on period in the fourth quarter method.

11.2. Hardware Resources

Both UART0 and UART1 have a length of 128 Byte hardware, read and write FIFO
operations are at the same address.
The hardware registers of two UART module are the same, and distinguished by macro
definitions of UART0 / UART1.
11.3. Parameter Configuration
UART attribute parameters are all in UART_CONF0 register, can be found in the
Uart_register.h. You can configure UART properties through modifying the different bit of
the register.

11.3.1. The Baud Rate

The serial of ESP8266 can support the baud rate range from 300 to 115200 * 40.
Espressif
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61 86 ! /!
11. UART Introduction
2016.05