What does UART mean?

UART: universal asynchronous receiver/transmitter, universal asynchronous receiver/transmitter. UART is a chip with parallel input and serial output, which is usually integrated on the motherboard, and most of them are 16550AFN chips. Because the computer uses parallel data, it can't directly send the data to the modem, and it must be sorted by UART before asynchronous transmission. The process is as follows: CPU first puts the data to be written into UART register (temporary storage block), and then transmits it to serial device through FIFO (first in first out queue). If there is no FIFO, the information will be confused and cannot be transmitted to the modem.

It is a chip for controlling computers and serial devices. It should be noted that it provides an RS-232C data terminal interface, so that computers can communicate with modems or other serial devices using the RS-232C interface. As a part of the interface, UART also provides the following functions: converting parallel data transmitted inside the computer into output serial data stream. Convert serial data from the outside of the computer into bytes for use by devices that use parallel data inside the computer. Add parity bits to the output serial data stream and check the parity of the data stream received from the outside. Add start-stop tags to the output data stream and delete the start-stop tags from the received data stream. Handle interrupt signals sent by keyboard or mouse (keyboard and mouse are also serial devices). Can deal with synchronization management between computer and external serial devices. Some high-end UART also provide buffers for input and output data. At present, the relatively new UART is 16550. Before the computer needs to process data, its buffer can store 16 bytes of data, while the usual UART is 8250. Now, if you buy a built-in modem, this modem usually contains 16550 UART.

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What is UART?

UART is a universal serial data bus for asynchronous communication. The bus can communicate in both directions and realize full duplex transmission and reception. In embedded design, UART is used to communicate with PC, including monitoring debugger and other devices, such as EEPROM.

UART communication

UART first converts the received parallel data into serial data for transmission. A message frame starts with a low-order start bit, followed by 7 or 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 for transmission and tries to synchronize with the transmitter clock frequency. If parity is selected, UART will add parity bits after the data bits. Parity bits can be used to help with error checking.

During the receiving process, UART deletes the start bit and end bit from the message frame, performs parity check on the input 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, UART will set the parity flag.

Data direction and communication speed

Data transmission can start from least significant bit (LSB). However, some UART allow flexible choice of sending least significant bit or most significant bit (MSB) first.

The data transmission speed of UART in microcontroller ranges from several hundred bits per second to1.5mb. For example, the speed of high-speed UART communication embedded in ElanSC520 microcontroller can be as high as1.1152mbps. The baud rate of UART is also affected by the distance (line length) between the transmitting line and the receiving line.

At present, there are two kinds of hardware on the market that only support asynchronous communication, and also support asynchronous and synchronous communication, which can be used for UART. The former is the meaning of UART name itself, which is called serial communication interface (SCI) in Motorola microcontroller. Universal Synchronous Asynchronous Receiver (USART) in microchip microcontroller and UART in Fujitsu microcontroller are two typical examples of the latter.

UART in computer

UART is the key part of computer serial communication port. In a computer, UART is connected to a circuit that generates a signal compatible with RS232 specification. The RS232 standard stipulates that the logic "1" signal is 3 to 25 volts relative to the ground, while the logic "0" is -3 to -25 volts relative to the ground. Therefore, when the UART in the microcontroller is connected to the PC, it needs an RS232 driver to convert the level.