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4. Peripheral Interface

Data transfers to/from UART interfaces can be implemented via hardware. The data

transmission speed via UART interfaces reaches 115200 x 40 (4.5 Mbps).

UART0 can be used for communication. It supports flow control. Since UART1 features

only data transmit signal (TX), it is usually used for printing log.

4.7. Pulse-Width Modulation (PWM)

ESP8285 has four PWM output interfaces. They can be extended by users themselves.

The pin definitions of the PWM interfaces are defined as below.

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 reaches as high as 44 ns. PWM frequency range is

adjustable from 1000 μs to 10000 μs, i.e., between 100 Hz and 1 kHz. When the PWM

frequency is 1 kHz, the duty ratio will be 1/22727, and a resolution of over 14 bits will be

achieved at 1 kHz refresh rate.

Table 4-6. Pin Definitions of UART

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

���� Note:

By default, UART0 outputs some printed information when the device is powered on and booting up. The

baud rate of the printed information is relevant to the frequency of the external crystal oscillator. If the

frequency of the crystal oscillator is 40 MHz, then the baud rate for printing is 115200; if the frequency of

the crystal oscillator is 26 MHz, then the baud rate for printing is 74880. If the printed information exerts

any influence on the functionality of the device, it is suggested to block the printing during the power-on

period by changing (U0TXD, U0RXD) to (MTDO, MTCK).

Table 4-7. Pin Definitions of PWM

Pin Name

Pin Num

IO

Function Name

MTDI

10

IO12

PWM0

MTDO

13

IO15

PWM1

MTMS

9

IO14

PWM2

GPIO4

16

IO4

PWM3

Espressif

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2018.12