UART Echo Example

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

This example demonstrates how to utilize UART interfaces of ESP32 by echoing back to the sender any data received on UART1.

How to use example

Hardware Required

The example can be run on any ESP32 development board connected to a PC 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.

Setup the Hardware

Connect the external serial interface to the ESP32 board as follows.

ESP32 Interface	#define	ESP32 Pin	External UART Pin
Transmit Data (TxD)	ECHO_TEST_TXD	GPIO4	RxD
Receive Data (RxD)	ECHO_TEST_RXD	GPIO5	TxD
Ground	n/a	GND	GND

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.

ESP32 Interface	#define	ESP32 Pin	External UART Pin
Request to Send (RTS)	ECHO_TEST_RTS	GPIO18	CTS
Clear to Send (CTS)	ECHO_TEST_CTS	GPIO19	RTS

Configure the project

make menuconfig

idf.py menuconfig

Set serial port under Serial Flasher Options.

Build and Flash

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

make -j4 flash monitor

idf.py 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.

Example Output

Type some characters in the terminal connected to the external serial interface. As result you should see echo in the terminal which is used for flashing and monitoring. You can verify if the echo indeed comes from ESP32 by disconnecting either TxD or RxD pin: no characters will appear when typing.

Troubleshooting

You are not supposed to see the echo in the terminal which is used for flashing and monitoring, but in the other one which is connected to UART1.

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