(See the README.md file in the upper level 'examples' directory for more information about examples.)

This example demonstrates how to utilize UART interfaces by echoing back to the sender any data received on configured UART.

The example can be run on any ESP32, ESP32-S and ESP32-C series based development board connected to a computer with a single USB cable for flashing and monitoring. The external interface should have 3.3V outputs. You may use e.g. 3.3V compatible USB-to-Serial dongle.

Connect the external serial interface to the board as follows.

  ---------------------------------------------------------------------------------------
  | Target chip Interface | #define          | Default ESP Pin      | External UART Pin |
  | ----------------------|------------------|----------------------|--------------------
  | Transmit Data (TxD)   | EXAMPLE_UART_TXD | GPIO4                | RxD               |
  | Receive Data (RxD)    | EXAMPLE_UART_RXD | GPIO5                | TxD               |
  | Ground                | n/a              | GND                  | GND               |
  ---------------------------------------------------------------------------------------

Note: Some GPIOs can not be used with certain chips because they are reserved for internal use. Please refer to UART documentation for selected target.

Optionally, you can set-up and use a serial interface that has RTS and CTS signals in order to verify that the hardware control flow works. Connect the extra signals according to the following table, configure both extra pins in the example code by replacing existing UART_PIN_NO_CHANGE macros with the appropriate pin numbers and configure UART1 driver to use the hardware flow control by setting .flow_ctrl = UART_HW_FLOWCTRL_CTS_RTS and adding .rx_flow_ctrl_thresh = 122.

  --------------------------------------------------------------------------------------
  | Target chip Interface | #define         | Default ESP Pin      | External UART Pin |
  | ----------------------|-----------------|----------------------|--------------------
  | Transmit Data (TxD)   | ECHO_TEST_RTS   | GPIO18               | CTS               |
  | Receive Data (RxD)    | ECHO_TEST_CTS   | GPIO19               | RTS               |
  | Ground                | n/a             | GND                  | GND               |
  --------------------------------------------------------------------------------------

Use the command below to configure project using Kconfig menu as showed in the table above. The default Kconfig values can be changed such as: EXAMPLE_TASK_STACK_SIZE, EXAMPLE_UART_BAUD_RATE, EXAMPLE_UART_PORT_NUM (Refer to Kconfig file).

idf.py menuconfig

Build the project and flash it to the board, then run monitor tool to view serial output:

idf.py -p PORT flash monitor

(To exit the serial monitor, type Ctrl-].)

See the Getting Started Guide for full steps to configure and use ESP-IDF to build projects.

Type some characters in the terminal connected to the external serial interface. As result you should see echo in the same terminal which you used for typing the characters. You can verify if the echo indeed comes from ESP board by disconnecting either TxD or RxD pin: no characters will appear when typing.

You are not supposed to see the echo in the terminal which is used for flashing and monitoring, but in the other UART configured through Kconfig can be used.