Data Sheet
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Espressif Systems
ESP8266 Datasheet
Table 13 Pin Definitions of UART Interfaces
Data transfers to/from UART interfaces can be implemented via hardware. The data transmission
speed via UART interfaces can reach 115200*40 (4.5Mbps).
UART0 can be for communication. It supports fluid control. Since UART1 features only data transmit
signal (Tx), it is usually used for printing log.
Notes: By default, UART0 will output some printed information when the device is powered on and is
booting up. The baud rate of the printed information is closely related to the frequency of the
external crystal oscillator. If the frequency of the crystal oscillator is 40MHz, then the baud rate for
printing is 115200; if the frequency of the crystal oscillator is 26MHz, then the baud rate for printing
is 74880. If the printed information exerts any influence on the functionality of your device, you’d
better block the printing during the power-on period by changing (U0TXD,U0RXD) to (MTDO,MTCK).
3.7. Pulse-Width Modulation (PWM)
Four PWM output interfaces have been defined by ESP8266EX. They can be extended by users
themselves. The present pin definitions of the PWM interfaces are defined as below:
Table 14 Pin Definitions of PWM Interfaces
The functionality of PWM interfaces can be implemented via software programming. For example, in
the LED smart light demo, the function of PWM is realized by interruption of the timer, the minimum
resolution can reach as much as 44 ns. PWM frequency range is adjustable from 1000 us to 10000 us,
Pin Type
Pin Name
Pin Num
IO
Function Name
UART0
U0RXD
25
IO3
U0RXD
U0TXD
26
IO1
U0TXD
MTDO
13
IO15
U0RTS
MTCK
12
IO13
U0CTS
UART1
GPIO2
14
IO2
U1TXD
SD_D1
23
IO8
U1RXD
Pin Name
Pin Num
IO
Function Name
MTDI
10
IO12
PWM0
MTDO
13
IO15
PWM1
MTMS
9
IO14
PWM2
GPIO4
16
IO4
PWM3
Espressif Systems / August 1, 2015
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