What is UART?

Universal Asynchronous Receiver / Transmitter, commonly called UART, is a universal serial data bus for asynchronous communication. The data to be transmitted is converted between serial communication and parallel communication. As a chip that converts parallel input signals into serial output signals, UART is usually integrated on the connection of other communication interfaces.

UART is a universal serial data bus for asynchronous communication. The bus has two-way communication and can realize full-duplex transmission and reception. In embedded design, UART is used for communication between host and auxiliary equipment, such as communication between car audio and external AP. Communication with PC includes communication with monitoring debugger and other devices, such as EEPROM.

Interface：

The UART can be said to be the most basic configuration in a single-chip computer. Many devices that communicate with computers use it. According to the most conventional description of computers, it is serial communication.

TX-data transmission interface;

RX-data receiving interface.

Connect TX to RX between the two devices, and connect RX to TX to work normally. The most commonly used is the USB on our computer, which is the most typical UART interface.

Application：

Communication field

The UART first converts the received parallel data into serial data for transmission. The message frame starts with a low-order start bit, followed by 5-8 data bits, an available parity bit, and one or more high-order stop bits. When the receiver finds the start bit, it knows that the data is ready to send and tries to synchronize with the transmitter clock frequency. If parity is selected, the UART adds the parity bit after the data bit. Parity bits can be used to help error checking.

During the receiving process, the UART removes the start and end bits from the message frame, performs parity check on the incoming bytes, and converts the data bytes from serial to parallel. The UART also generates additional signals to indicate the status of transmission and reception. For example, if a parity error occurs, the UART sets the parity flag. Parity bits are used to verify that the transmission is correct.

Computer

UART is a key part of the serial communication port in a computer. In a computer, the UART is connected to a circuit that generates RS232-compliant signals. The RS232 standard defines a logic "1" signal as -3 to -15 volts with respect to ground and a logic "0" as +3 to +15 volts with respect to ground. Therefore, when a UART in a microcontroller is connected to a PC, it requires an RS232 driver to switch levels.

Uart here refers to the TTL level serial port; RS232 refers to the RS232 level serial port.

The TTL level is 5V, while RS232 is a negative logic level. It defines + 5 ~ + 12V as low level, and -12 ~ -5V as high level.

Uart serial ports such as RXD and TXD are generally directly connected to the pins of the processor chip, while RS232 serial ports RXD and TXD etc. generally require level conversion (usually level conversion by chips such as Max232) to be connected to the processor chip Pin, otherwise such a high voltage is likely to burn out the chip.

The serial port of the computer we usually use is RS232. When we are doing circuit work, we should pay attention to whether the serial port of the peripheral is Uart or RS232. If it does not match, we should find a conversion line (usually this conversion line) There is a chip similar to the Max232 chip for level conversion). You cannot blindly connect the two serial ports.