How does a Universal Asynchronous Receiver/Transmitter (UART) facilitate asynchronous data communication?
1 Answer
A Universal Asynchronous Receiver/Transmitter (UART) is a popular hardware communication protocol used to facilitate asynchronous data communication between two devices. The key feature of UART that enables asynchronous communication is its use of start and stop bits, along with a predefined baud rate. Here's how UART achieves asynchronous data communication:
Baud rate: The baud rate is the speed at which data is transmitted over the UART interface. It represents the number of bits transmitted per second. Both the transmitting and receiving devices must be configured to operate at the same baud rate for successful communication. The agreed-upon baud rate ensures that both devices synchronize their internal clocks to understand when each bit is transmitted or received.
Start bit: When the UART transmitter has data to send, it initiates the transmission by sending a start bit. The start bit is always at a low voltage level (0) and marks the beginning of a new data frame. The receiver watches the incoming data line and waits for the start bit to detect the beginning of the data frame.
Data bits: Following the start bit, the UART transmitter sends the actual data bits (usually 8 bits) one by one. The data is sent least significant bit (LSB) first. The receiver samples each bit at regular intervals determined by the baud rate to read the data correctly.
Parity bit (optional): Some UART configurations include a parity bit. The parity bit provides a basic error-checking mechanism. It can be set to either odd or even parity based on the number of 1s in the data bits. If used, the transmitter includes the parity bit after the data bits.
Stop bit(s): After the data and optional parity bits, the UART transmitter sends one or more stop bits. The stop bit(s) are always at a high voltage level (1). The stop bit indicates the end of the data frame and allows the receiver to prepare for the next frame.
Asynchronous nature: The term "asynchronous" in UART refers to the fact that there is no common clock shared between the transmitter and receiver to keep them perfectly in sync. Instead, the receiving device relies on the start bit to know when a new frame is beginning. Once the start bit is detected, the receiver uses the predetermined baud rate to sample the incoming data bits and reconstruct the transmitted data frame.
Due to its simplicity and widespread support, UART is commonly used in many embedded systems, microcontrollers, and various communication interfaces where asynchronous data transfer is required. However, one drawback of UART is that it does not provide flow control, which means data overrun may occur if the receiving device can't process the incoming data quickly enough. To overcome this limitation, hardware flow control (using additional control lines like RTS/CTS) or software flow control (using XON/XOFF characters) may be implemented.
Baud rate: The baud rate is the speed at which data is transmitted over the UART interface. It represents the number of bits transmitted per second. Both the transmitting and receiving devices must be configured to operate at the same baud rate for successful communication. The agreed-upon baud rate ensures that both devices synchronize their internal clocks to understand when each bit is transmitted or received.
Start bit: When the UART transmitter has data to send, it initiates the transmission by sending a start bit. The start bit is always at a low voltage level (0) and marks the beginning of a new data frame. The receiver watches the incoming data line and waits for the start bit to detect the beginning of the data frame.
Data bits: Following the start bit, the UART transmitter sends the actual data bits (usually 8 bits) one by one. The data is sent least significant bit (LSB) first. The receiver samples each bit at regular intervals determined by the baud rate to read the data correctly.
Parity bit (optional): Some UART configurations include a parity bit. The parity bit provides a basic error-checking mechanism. It can be set to either odd or even parity based on the number of 1s in the data bits. If used, the transmitter includes the parity bit after the data bits.
Stop bit(s): After the data and optional parity bits, the UART transmitter sends one or more stop bits. The stop bit(s) are always at a high voltage level (1). The stop bit indicates the end of the data frame and allows the receiver to prepare for the next frame.
Asynchronous nature: The term "asynchronous" in UART refers to the fact that there is no common clock shared between the transmitter and receiver to keep them perfectly in sync. Instead, the receiving device relies on the start bit to know when a new frame is beginning. Once the start bit is detected, the receiver uses the predetermined baud rate to sample the incoming data bits and reconstruct the transmitted data frame.
Due to its simplicity and widespread support, UART is commonly used in many embedded systems, microcontrollers, and various communication interfaces where asynchronous data transfer is required. However, one drawback of UART is that it does not provide flow control, which means data overrun may occur if the receiving device can't process the incoming data quickly enough. To overcome this limitation, hardware flow control (using additional control lines like RTS/CTS) or software flow control (using XON/XOFF characters) may be implemented.