What are the main scenarios of UART serial communication? (How does it work?) ）

Overview of UART Serial Communication

UART (Universal Asynchronous Receiver/Transmitter) serial communication is a common communication technology for single-chip microcomputers. It is usually used for data exchange between single-chip microcomputers or between single-chip microcomputers and computers. UART communication doesn't require a clock signal and can achieve full-duplex transmission and reception, meaning that data can be sent and received simultaneously.

Features of UART Serial Communication

The features of UART serial communication include:

• Simple Hardware Connection: Usually, only two wires are needed, one for sending data (TX) and one for receiving data (RX).
• Flexible Communication Methods: Data can be sent and received through polling, interrupt, or DMA (Direct Memory Access) methods.
• Multiple Communication Protocols: It can support multiple communication protocols, such as RS-232, RS-422, RS-485, etc.
• Easy to Program: Most microcontrollers and operating systems provide APIs for UART communication, facilitating developers to program.

Programming Methods of UART Serial Communication

The main programming methods of UART serial communication are as follows:

• Polling Method: Continuously poll the status of the UART communication register to determine whether the data is ready to be sent or received.
• Interrupt Method: Set the interrupt enable bit. When the data is ready, the CPU will automatically respond to the interrupt and execute the corresponding interrupt service routine.
• DMA Method: The DMA controller directly transfers data between memory and peripherals to reduce the burden on the CPU.

Precautions for UART Serial Communication

When using UART serial communication, the following points need to be noted:

• Baud Rate Matching: The baud rates of the transmitting end and the receiving end must be the same; otherwise, communication failure will occur.
• Level Conversion: Different devices may have different level standards, and level conversion chips may be needed for adaptation.
• Flow Control: In high-speed communication, hardware or software flow control may be required to prevent data loss.

UART serial communication is a simple and efficient communication method, suitable for data exchange in various embedded systems and communication devices. In practical applications, developers need to choose the appropriate programming method according to specific communication requirements and pay attention to relevant configurations and precautions to ensure the reliability and efficiency of communication.

Working Principle of UART Serial Communication

UART (Universal Asynchronous Receiver/Transmitter) is a serial communication interface commonly used for communication between chips in a system. It can achieve two-way data transmission without a common clock signal. Instead, data is transmitted at a pre-agreed baud rate, so it is relatively simple in circuit implementation and has low cost.

• Data Transmission Format: The data transmission format of the UART communication protocol includes start bits, data bits, parity check bits (optional), and stop bits. The start bit is usually a logic "0" signal, indicating the start of the transmission of a character. The number of data bits can be 4, 5, 6, 7, or 8, etc., forming a character, usually in ASCII code. The parity check bit is used to check the correctness of data transmission and can be even parity or odd parity. The stop bit is the end mark of a character's data and can be 1 bit, 1.5 bits, or 2 bits of high level.

• Working Principle: During the data sending process, the line is at a high level in the idle state. When a sending instruction is received, the time T of one data bit on the line is pulled low, and then the data is sent from the low bit to the high bit in sequence. After the data is sent, the parity check bit and the stop bit are sent, and the transmission of one frame of data is completed. During the data receiving process, the line is also at a high level in the idle state. When the falling edge of the line (changing from high level to low level) is detected, it indicates that there is data transmission on the line. The data is received from the low bit to the high bit according to the agreed baud rate. After the data is received, the parity check bit is received and compared to check whether it is correct. If it is correct, the subsequent devices are notified to receive the data or store it in the buffer.

• Clock Synchronization: Since UART is asynchronous transmission without a transmission synchronization clock, to ensure the correctness of data, UART uses a clock with 16 times the data baud rate for sampling. Each data has 16 clock samples, and the middle sample value is taken to ensure that there is no slip code or error code in sampling. Generally, the number of data bits in one frame of UART is 8, so that even if there is an error of one clock for each data, the receiving end can correctly sample the data.

Application Scenarios of UART Serial Communication

UART (Universal Asynchronous Receiver/Transmitter) is a communication protocol widely used between microcontrollers, computers, and other digital devices. The following are some common application scenarios of UART serial communication:

• Data Exchange in Embedded Systems: UART is often used for data exchange between microcontrollers in embedded systems. For example, in a smart home system, different sensors and controllers may communicate through the UART interface to achieve data sharing and collaborative work.
• Communication between Devices and Computers: UART can realize communication between devices and computers through USB-to-UART chips. This is particularly important in embedded system development because developers can send the device's running status, error information, etc. to the computer for analysis and processing through tools such as serial port debugging assistants.
• Connecting Various Modules: The UART interface can connect various external modules, such as GPS modules, Bluetooth modules, WiFi modules, etc. For example, GPS modules usually output data in the NMEA standard format through the UART interface, and these data can be received and parsed by the main system to achieve functions such as position tracking.
• Simple Data Exchange between Devices: In some simple devices, UART can be used as a low-cost and simple communication method. For example, only three wires, TX, RX, and GND, need to be connected between two microcontrollers to achieve basic data exchange.
• Connecting Display Terminals: UART can connect display terminals, such as LCD display screens, to display the system's running information, menu options, etc. to users. This is very common in some small devices or industrial control devices.
• Communication with Industrial Equipment: In industrial automation control systems, UART communication is used for data exchange and control instruction transmission between devices. For example, PLC (Programmable Logic Controller) may communicate with other devices through the UART interface to achieve control and monitoring of the industrial production process.
• As a Debugging Interface: In embedded system development, UART is often used as a low-cost debugging interface. Developers can obtain the device's startup logs and error information or input commands to interact with the device by connecting to the PC's serial console.
• Internet of Things Applications: The UART serial WiFi module can achieve arbitrary transparent conversion among the user serial port, Ethernet, and wireless network (WiFi) interfaces, enabling traditional serial port devices to better join wireless networks. This is particularly important in fields such as smart homes, smart buildings, smart cities, and smart industries.
• Automotive Communication: In automotive electronic systems, UART communication is used for data transmission between various controllers and sensors. For example, the engine control unit (ECU) may communicate with other sensors and actuators through UART.
• Remote Control and Monitoring: The UART interface can be used for remote control and monitoring applications. By connecting to remote devices through the UART interface, real-time control and monitoring of the devices can be achieved.

Commonly Used Communication Protocols in UART Serial Communication

The UART (Universal Asynchronous Receiver/Transmitter) serial communication protocol is a commonly used communication protocol. It supports full-duplex communication, that is, it supports both data sending and receiving simultaneously. The UART protocol defines start bits, data bits, optional parity check bits, and stop bits. The start bit is used to mark the start of data transmission, the data bits contain the actual data to be transmitted, the parity check bit is used for simple error detection, and the stop bit marks the end of data transmission.

• RS-232: RS-232 is a common serial communication protocol used for data transmission between computers and external devices. It defines parameters such as the format of data frames, baud rates, and check bits. The RS-232 protocol is simple and commonly used, but its effective transmission distance is short, and it can only perform one-to-one communication.
• RS-485: RS-485 is a multi-point communication protocol that allows serial communication among multiple devices. It is usually used in industrial control and automation fields. The data signal of RS-485 adopts a differential transmission mode, also known as balanced transmission. It uses a pair of twisted pairs, which can solve the problem of the short communication distance of RS-232 and can achieve one-to-many communication.
• Modbus: Modbus is a commonly used industrial communication protocol for communication between devices in control systems. It defines a series of data frame formats and communication procedures and is widely used in the industrial automation field.

All of the above protocols can be used for UART serial communication, and they each have their own characteristics and are suitable for different communication requirements and application scenarios.

How to Solve the Baud Rate Mismatch Problem in UART Serial Communication

When solving the baud rate mismatch problem in UART serial communication, the following aspects usually need to be considered:

1. Confirm the Baud Rate Settings

First, it is necessary to confirm whether the baud rate settings of the transmitting end and the receiving end are the same. If the baud rate settings of the two do not match, data transmission will be incorrect, resulting in the inability to correctly parse the received data.

2. Check the Clock Source and Divider Settings

Second, it is necessary to check whether the clock source and divider settings used for UART communication are correct. For example, in the STM32 series of microcontrollers, the baud rate calculation formula for UART is UART_BRR = ((clock frequency) / ((baud rate) * 16)) - 1. If the clock frequency or divider settings are improper, the actual baud rate will not match the expected baud rate.

3. Hardware Connection and Signal Integrity

In addition, it is necessary to check whether the hardware connection is correct and whether there is interference or attenuation during signal transmission. These factors may also lead to inaccurate baud rate measurement.

4. Software Configuration and Programming Errors

In terms of software configuration and programming, it is necessary to ensure that there are no logical errors or configuration errors. For example, in some cases, specific registers may need to be configured to ensure that UART can work at the correct baud rate.

5. Use Professional Tools for Detection

If the above methods cannot solve the problem, professional serial communication test tools can be considered to detect and diagnose the problem. These tools can help accurately measure the actual baud rate and provide detailed communication status information.

In summary, solving the baud rate mismatch problem in UART serial communication requires comprehensive consideration of multiple aspects such as hardware settings, software configuration, clock source, and divider settings. Through careful inspection and adjustment, the root cause of the problem can usually be found and solved.

Summary

UART serial communication is a common communication technology for single-chip microcomputers. It has features such as simple hardware connection and flexible communication methods. It has various programming methods, and its working principle involves data transmission format and other contents. It has a wide range of application scenarios and multiple communication protocols. Attention should be paid to issues such as baud rate matching, and problems can be solved from multiple aspects when they occur.