STM32 Microcontroller UART Communication Guide: In-depth Analysis of the UART Protocol, Configuration, and Application, Easily Achieving Serial Communication

# STM32 Microcontroller UART Communication Guide: In-depth on UART Protocol, Configuration, and Application

## 1. UART Communication Basics

UART (Universal Asynchronous Receiver/Transmitter) is a serial communication protocol used for data transfer between two devices. It is widely used in embedded systems to communicate with peripheral devices such as sensors, displays, and keyboards.

UART communication is based on asynchronous transmission, meaning that data is transferred at an不定 rate, and the sender and receiver use different clocks. Data is transferred serially, one bit at a time, via one or two wires (one for sending and one for receiving).

## 2. UART Protocol and Configuration

### 2.1 Detailed UART Protocol

UART (Universal Asynchronous Receiver/Transmitter) is a serial communication protocol used for data transfer between two devices. It employs asynchronous transmission mode, meaning that there is no fixed time relationship between data bits, and each byte includes a start bit, data bits, an optional parity bit, and stop bits.

The frame format of the UART protocol is as follows:

| Field | Bit Count | Description |
|---|---|---|
| Start Bit | 1 | Low电平，标志着帧的开始 |
| Data Bits | 5-8 | The data being transferred, typically 8 bits |
| Parity Bit (Optional) | 1 | Parity bit used for error detection in transmission |
| Stop Bit | 1-2 | High电平，标志着帧的结束 |

### 2.2 STM32 Microcontroller UART Configuration

#### 2.2.1 Clock Configuration

UART communication requires a clock source to generate baud rates. For STM32 microcontrollers, either the system clock or an external clock source can be used.

/* Use system clock as UART clock source */
RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1, ENABLE);

/* Use external clock source as UART clock source */
RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1, DISABLE);
RCC_USARTCLKConfig(RCC_USART1, RCC_USARTClockSource_SYSCLK);

#### 2.2.2 Pin Configuration

UART communication requires two pins: one for sending data (TX) and another for receiving data (RX).

/* Configure USART1 TX pin */
GPIO_InitTypeDef GPIO_InitStructure;
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_Init(GPIOA, &GPIO_InitStructure);

/* Configure USART1 RX pin */
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_10;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;
GPIO_Init(GPIOA, &GPIO_InitStructure);

#### 2.2.3 Baud Rate Configuration

The baud rate is the number of bits transmitted per second in UART communication. The STM32 microcontroller can configure the baud rate by setting the UART baud rate registers.

/* Set USART1 baud rate to 115200 */
USART_InitTypeDef USART_InitStructure;
USART_InitStructure.USART_BaudRate = 115200;
USART_Init(USART1, &USART_InitStructure);

#### 2.2.4 Data Format Configuration

The data format defines the number of data bits, parity type, and the number of stop bits in UART communication. The STM32 microcontroller can configure the data format by setting the UART data format registers.

/* Set USART1 data format to 8 data bits, no parity, and 1 stop bit */
USART_InitStructure.USART_WordLength = USART_WordLength_8b;
USART_InitStructure.USART_Parity = USART_Parity_No;
USART_InitStructure.USART_StopBits = USART_StopBits_1;
USART_Init(USART1, &USART_InitStructure);

## 3. UART Communication in Practice

### 3.1 UART Data Transmission

**Data transmission process:**

1. **Initialize the UART peripheral:** Configure parameters such as the clock, pins, and baud rate.
2. **Prepare the data:** Store the data to be sent in a buffer.
3. **Check if the transmit buffer is empty:** If it is, you can start sending data.
4. **Write data to the transmit register:** Use the `UART_SendData()` function to write data to the UART transmit register.
5. **Wait for transmission to complete:** Poll the `UART_GetFlagStatus()` function and check if the `UART_FLAG_TXE` flag is set, indicating t