The Universal Asynchronous Receiver/Transmitter (UART) is a ubiquitous communication protocol used for serial data transmission. It finds wide application in embedded systems, computer peripherals, and other applications where simple, flexible data exchange is required. While the UART protocol itself is fairly standardized, there are various UART standards that dictate the specific electrical, timing, and signaling characteristics for different applications. These standards ensure compatibility between devices and guarantee reliable data transfer.
UART Standards: Ensuring Interoperability
The most common UART standard, and the one typically referred to simply as "UART," is the RS-232 standard. This standard, developed by the Electronic Industries Alliance (EIA), defines the electrical characteristics for serial communication over a two-wire interface. The RS-232 standard specifies voltage levels, data rates, and other parameters to ensure reliable data transfer between devices.
Other Popular UART Standards:
While the RS-232 standard is widely used, other UART standards have emerged to meet specific needs and address limitations of the original standard. Here are some popular UART standards:
RS-422: This standard provides a balanced differential signaling scheme, which significantly improves noise immunity and allows for longer transmission distances. RS-422 is well-suited for industrial applications and environments where electrical noise is a concern.
RS-485: Similar to RS-422, RS-485 employs balanced differential signaling and allows for multiple devices to share the same communication bus in a multi-drop configuration. This makes it an ideal choice for applications requiring communication between multiple devices, such as industrial control systems or sensor networks.
TTL (Transistor-Transistor Logic) Level UART: This is a common standard used in embedded systems and microcontrollers. It operates at lower voltage levels compared to RS-232, making it more power efficient and suitable for close-proximity communication.
USB (Universal Serial Bus) UART: USB is a widely used standard for connecting peripherals to computers. It allows for data transfer over a single cable and can support a wide range of devices. Some USB UART devices use a UART protocol internally to communicate with the host computer.
Choosing the Right UART Standard:
The choice of UART standard depends on the specific application requirements, including:
- Data Rate: The speed at which data is transferred.
- Transmission Distance: The distance between the communicating devices.
- Noise Immunity: The ability to withstand electrical noise.
- Number of Devices: The number of devices that need to communicate on the same bus.
- Power Consumption: The amount of power required to operate the interface.
RS-232 is suitable for short-range communication with a single device and is often used for basic applications, such as connecting a modem to a computer. RS-422 is suitable for longer-range communication and applications requiring high noise immunity. RS-485 is ideal for applications where multiple devices need to communicate over a single bus. TTL-level UART is commonly used in embedded systems and microcontrollers for short-range, low-power applications. USB UART provides high data rates and is ideal for connecting peripherals to computers.
Implementation:
UART communication typically involves a UART transceiver chip, which handles the conversion between parallel data and serial data. The transceiver provides the necessary logic levels, timing, and control signals for the communication.
UART Communication Protocol:
UART communication follows a serial protocol based on asynchronous data transmission. This means that the data is transmitted one bit at a time and there is no shared clock signal between the communicating devices. The following steps describe the UART communication protocol:
- Start Bit: The communication begins with a start bit, which is a logic low signal that alerts the receiver that data transmission is about to begin.
- Data Bits: The actual data bits are transmitted sequentially, starting with the least significant bit (LSB) and ending with the most significant bit (MSB).
- Parity Bit: An optional parity bit can be transmitted after the data bits to detect errors in the transmission.
- Stop Bit: The communication ends with a stop bit, which is a logic high signal indicating the end of the transmission.
The number of data bits, the parity bit, and the number of stop bits can be configured to suit the application requirements.
UART Communication in Microcontrollers:
Many microcontrollers have built-in UART peripherals that simplify the implementation of serial communication. The microcontroller's UART peripheral handles the transmission and reception of data, relieving the programmer of the need to manage the timing and signaling details.
Example Code for UART Communication in a Microcontroller:
#include
void main() {
// Initialize UART peripheral
TRISCbits.TRISC6 = 1; // Set TX pin as output
TRISCbits.TRISC7 = 0; // Set RX pin as input
RCSTA = 0x90; // Enable TX and RX, 8-bit data, no parity
SPBRG = 25; // Set baud rate to 9600
// Send data to UART
TXREG = 'A'; // Send character 'A'
while(!TXIF); // Wait for TX buffer to empty
// Read data from UART
while(!RCIF); // Wait for data to be received
char data = RCREG; // Read data from RX buffer
while(1);
}
This code snippet shows a basic example of UART communication in a microcontroller. The code initializes the UART peripheral, sends a character to the UART, and then reads a character received from the UART. The specific register names and settings may vary depending on the microcontroller used.
Conclusion:
UART is a versatile and widely used serial communication protocol that enables simple and reliable data exchange between devices. The various UART standards provide different electrical, timing, and signaling characteristics to meet specific application requirements. Understanding these standards is essential for choosing the right interface for your application and ensuring compatibility between devices. The choice of UART standard depends on factors such as data rate, transmission distance, noise immunity, number of devices, and power consumption. By carefully selecting the appropriate UART standard, you can ensure robust and efficient data communication in your systems.