Basics of Peripheral Control with ESP32: UART Communication

1. Basic Concepts of UART

UART (Universal Asynchronous Receiver/Transmitter) is a universal asynchronous transceiver with the following characteristics:

• Asynchronous Communication: No clock line is required, only TX (transmit) and RX (receive) data lines are needed.
• Full-Duplex Transmission: Supports simultaneous data transmission and reception.
• Flexible Configuration: Baud rate, data bits, parity bits, and stop bits can be set.

Typical Application Scenarios

• Serial debugging output (replacing printf)
• Communication with GPS, Bluetooth, and WiFi modules
• Interaction with PC host or other microcontrollers

2. ESP32 UART Hardware Features

The ESP32 integrates three UART controllers:

UART Number	Default Function	Configurability
UART0	Firmware download and debugging output	Pin can be remapped
UART1	Typically used for peripheral communication	Pin can be remapped
UART2	General communication	Pin can be remapped

Key Features:

• Supports baud rate range: 110bps – 5Mbps
• Configurable data bits (5-8 bits), stop bits (1/1.5/2 bits)
• Supports parity checking (even/odd/no parity)
• Supports hardware flow control (RTS/CTS)
• Supports interrupt and DMA transfer modes

3. ESP-IDF UART Programming Interface

1. Configuration Structure

typedef struct {
int baud_rate;              // Baud rate
uart_word_length_t data_bits; // Data bits
uart_parity_t parity;       // Parity bits
uart_stop_bits_t stop_bits; // Stop bits
uart_hw_flowcontrol_t flow_ctrl; // Hardware flow control
uint8_t rx_flow_ctrl_thresh; // Flow control threshold
} uart_config_t;

2. Common API Functions

Function	Description
<span>uart_driver_install()</span>	Install UART driver
<span>uart_param_config()</span>	Configure UART parameters
<span>uart_set_pin()</span>	Set TX/RX pins
<span>uart_write_bytes()</span>	Send data
<span>uart_read_bytes()</span>	Receive data
<span>uart_flush()</span>	Clear receive buffer

4. UART Communication Examples

1. Basic Sending Example

#include "driver/uart.h"
#include "esp_log.h"

#define UART_PORT_NUM    UART_NUM_1
#define UART_TX_PIN      GPIO_NUM_17
#define UART_RX_PIN      GPIO_NUM_16
#define BUF_SIZE         1024

void app_main(void) {
    // UART parameter configuration
    uart_config_t uart_config = {
        .baud_rate = 115200,
        .data_bits = UART_DATA_8_BITS,
        .parity    = UART_PARITY_DISABLE,
        .stop_bits = UART_STOP_BITS_1,
        .flow_ctrl = UART_HW_FLOWCTRL_DISABLE
    };

    // Install and configure UART
    uart_param_config(UART_PORT_NUM, &uart_config);
    uart_set_pin(UART_PORT_NUM, UART_TX_PIN, UART_RX_PIN,
                UART_PIN_NO_CHANGE, UART_PIN_NO_CHANGE);
    uart_driver_install(UART_PORT_NUM, BUF_SIZE, 0, 0, NULL, 0);

    // Send data
    const char *test_str = "Hello UART\n";
    while (1) {
        uart_write_bytes(UART_PORT_NUM, test_str, strlen(test_str));
        vTaskDelay(pdMS_TO_TICKS(1000));
    }
}

2. Data Reception Handling

uint8_t data[BUF_SIZE];
int len = uart_read_bytes(UART_PORT_NUM, data, BUF_SIZE, pdMS_TO_TICKS(1000));
if (len > 0) {
    data[len] = '\0';  // Add string terminator
    ESP_LOGI("UART", "Recv: %s", (char*)data);
}

3. Serial Echo Implementation

uint8_t data[BUF_SIZE];
while (1) {
    int len = uart_read_bytes(UART_PORT_NUM, data, BUF_SIZE, pdMS_TO_TICKS(100));
    if (len > 0) {
        uart_write_bytes(UART_PORT_NUM, (const char*)data, len); // Echo data
    }
}

5. Advanced Application Techniques

1. Automatic Baud Rate Detection:

• Automatically calculate baud rate by measuring the width of the start bit
• Applicable in situations where the target device’s baud rate is uncertain

DMA Transfer:

• Set rx_buffer and tx_buffer sizes when using <span>uart_driver_install()</span>
• Suitable for high-speed data transmission, reducing CPU load

Hardware Flow Control:

• Configure RTS/CTS pins to implement hardware flow control
• Prevents data loss, suitable for high-speed communication

Interrupt Handling:

• Register interrupt handler functions to handle specific events
• Such as frame errors, parity errors, etc.

6. Common Troubleshooting

1. No Data Transmission:

• Check if TX/RX pin connections are correct
• Ensure baud rate settings are consistent on both ends
• Verify that hardware connections are normal

Data Corruption:

• Check baud rate, data bits, stop bits, and parity settings
• Ensure good ground connection

Data Loss:

• Increase the size of the receive buffer
• Lower the baud rate or enable hardware flow control
• Check if the program processes received data in a timely manner