2.4 KiB
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
or
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
or
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.