Serial communication is a fundamental aspect of embedded systems, enabling efficient data transfer between microcontrollers and peripherals. The 8051 microcontroller supports two key serial communication protocols: UART (Universal Asynchronous Receiver/Transmitter) and SPI (Serial Peripheral Interface).
UART facilitates simple, asynchronous communication using just TX (Transmit) and RX (Receive) lines, making it ideal for direct device-to-device connections. On the other hand, SPI is a synchronous protocol that enables high-speed communication between a master and multiple slave devices using MOSI, MISO, SCK, and SS lines.
In this blog, we’ll explore how UART and SPI work in 8051, their configurations, and example implementations to help you integrate serial communication into your embedded projects.
One of the most important data transfer techniques in embedded systems is serial communication. Several serial communication protocols, such as SPI (Serial Peripheral Interface) and UART (Universal Asynchronous Receiver/Transmitter), are supported by the 8051 microcontroller. The fundamentals of 8051 microcontroller SPI and UART communication will be covered in this paper.
Compared to parallel communication, serial communication uses fewer wires and can communicate over long distances by sending data one bit at a time. SPI and UART are two serial communication protocols that are frequently used in embedded systems.
Asynchronous communication is facilitated by UART. TX (Transmit) and RX (Receive) are the two lines it uses to send and receive data. Synchronous communication is facilitated by SPI. Multiple data lines, including MOSI (Master Out Slave In), MISO (Master In Slave Out), SCK (Serial Clock), and SS (Slave Select), are used in a master-slave configuration.
2.1. What is UART?
A clock signal is not required for data transfer between two devices thanks to the asynchronous UART communication protocol. Start bits, data bits, optional parity bits, and stop bits make up each UART data frame. UART communication is supported by the 8051 by default.
2.2. Important Asynchronous UART Features: For synchronization, no clock signal is utilized. Baud Rate: The baud rate, which specifies the number of bits sent per second, determines the communication speed. Start and Stop Bits: To indicate the start and finish of data transmission, each data frame starts with a start bit and finishes with one or more stop bits. Parity: An optional error-checking bit that the data frame may include.
2.3. Setting up UART on an 8051
The Serial Control Register (SCON) is used by the 8051 to set up UART communication.
The SCON register’s essential bits are: The modes (e.g., Mode 1 for 8-bit variable baud rate) are set using SM0 and SM1.
REN: Bit for receiver enable. TI: Send the interrupt signal.
RI: Acquire the interrupt signal. Baud Rate: Usually, Timer 1 in the 8051 is used to set the baud rate. The baud rate is defined by the overflow rate of the Timer.
2.4. An Example of Basic UART Communication
Here is an illustration of how to set up and send data with the 8051’s UART:
In the code above:
Timer 1 is set up to produce the proper baud rate. The data is transmitted via the SBUF register. To verify that the byte has been sent, the TI flag is tracked.
2.5. Using UART to Receive Data
You keep an eye on the Receive Interrupt (RI) flag in order to receive data. The byte is saved in the SBUF register upon receiving data.
3.1. What is SPI?
For quick data transfer between a master device and one or more slave devices, synchronous serial protocol, or SPI, is utilized. It synchronizes data transmission between devices using a clock signal (SCK).
3.2. Essential Elements of Synchronous SPI:
The clock signal is used to synchronize data (SCK). In a master-slave configuration, one device controls the clock while the others serve as slaves.
3.3. Setting up SPI on an 8051
Since the 8051 lacks an integrated SPI interface, you will need to use external SPI modules or general-purpose I/O pins to implement SPI communication. The following procedures are necessary for the SPI protocol: Set the clock pin (SCK) so that it generates a clock signal at the appropriate frequency. Data Transfer: To send and receive data, use the MOSI and MISO pins. Slave Select: The active slave device is chosen using the slave select line.
3.4. An Example of Basic SPI Communication
Here is a basic illustration of data transmission via an SPI master.
This code sends data via the MOSI pin and toggles the clock line to mimic simple SPI data transmission.
4. In conclusion
In embedded systems, serial communication is crucial, and the 8051 microcontroller offers flexible data transfer via both SPI and UART protocols. SPI provides a quicker, synchronous way to communicate with numerous peripherals, whereas UART is best for easier, asynchronous communication between two devices. By comprehending both protocols and their setups, you can use the 8051 to create reliable and effective embedded systems.