What is UART in Plain English?

We often face the phrase universal asynchronous receiver-transmitter in matters like serial communication of Arduino or some shield’s of Arduino. What is UART in Plain English? UART is an electronic circuit used to implement digital serial interfaces of computer or peripheral devices. Serial transmission is commonly used for modems, non-networked communication between computers or peripherals. There are two forms of serial transmission – Synchronous and Asynchronous.

TTY interface can almost be described as prehistoric, more than 100 years old. Originally it was developed for the teletype network (TTY = Teletype). We are talking about ancient telegraph like matter – 0 and 1. The individual bits were associated with a character were sent in order (‘serial’). Each character to be sent was preceded by a START bit (log 0). This is followed by the bits of the character itself. The completion was followed by the parity bit and one to two STOP bits (log 1).

What is UART in Plain English?

UART can be either an independent electronic component like a chip or a part of a component like a microcontroller. Some of the microcontrollers can be programmed. Arduino has microcontrollers which can be programmed.

An UART interface is used to send and receive data over a data line and is the standard of serial interfaces on PCs, microcontrollers, and in the industrial sector, to interface with various interfaces.

The data is transmitted as a serial digital data stream with a fixed frame consisting of a start bit, five to a maximum of nine data bits, an optional parity bit for detecting transmission errors and a stop bit. In order to give the receiver a synchronization time to the clock of the received data, the stop bit can be extended to 1.5 or 2 times the normal transmission time of one bit. This is called 1.5 or 2 stop bits.

Baud is a measurement of transmission speed in asynchronous communication. Baud Rate represents the number of bits which are being sent, not the amount of data. At a baud rate of 300 baud, the maximum achievable data rate is 300/(7+3) = 30 characters per second.

Special feature in the asynchronous mode of operation is that, no separate clock signal is used on a transmission line. Instead, the receiver synchronizes over the length of the frame, mediated by the start and stop bits, as well as the set baud rate (which in this case corresponds to the bit rate ). Since the beginning of a transmission with the start bit can take place at arbitrary times, this serial interface becomes asynchronous designated. In order to ensure synchronization, the number of transferable bits is limited. With a longer data stream, the synchronization could be lost, which can lead to misinterpretations of the data stream and thus to a faulty transmission. Synchronous mode serial interfaces do not require a frame of start/stop bits, they ensure the synchronicity of the participants in other ways. For example, by using an extra clock line or the clock recovering from the line code.

Where This UART is Used?

A UART is usually implemented as a communication component in microcontrollers or computers, as a stand-alone integrated circuit, as a subfunction in chipsets, in the form of hardware description languages. It can be used as a so-called “software UART” Program sequence. The data to be transmitted or received are usually delivered to the UART in parallel form, for example via a CPU-external bus.

A UART device that has been used as a stand-alone device for many years in commercially available PCs is the National Semiconductor developed UART 8250 and its compatible successors. Since the mid-1990s, UART controllers in PCs are hardly used as independent integrated circuits, since the serial interfaces are housed in the chipset (southbridge) of the mainboard.

Advantages of UART is that it uses two wires, no clock signal is needed and is widely used method. Disadvantages of UART is the limit in the size of the data frame to a maximum of 9 bits and limit of baud rates of each UART which must be within 10% of each other.