Understanding Serial Communication Protocols

A complete guide to serial communication protocols, their uses, and how they work in embedded systems.

Introduction to Serial Communication

Serial communication is a technique used to send data between devices one bit at a time over a communication channel. It is widely used in embedded systems due to its simplicity and effectiveness in transmitting data over long distances. It is a key feature in many microcontrollers, computers, and other communication devices.

In this tutorial, we will cover the basics of serial communication, including different types of protocols, their practical uses, and how you can implement them in your projects.

Types of Serial Communication Protocols

1. UART (Universal Asynchronous Receiver-Transmitter)

UART is one of the simplest forms of asynchronous serial communication. It uses two lines, TX (transmit) and RX (receive), to send data between two devices without needing a clock signal. Since it's asynchronous, both devices need to agree on a data rate (baud rate) and data format (number of bits, parity, etc.) before communication can begin.

Key Features of UART:

Example UART Code (Arduino):


// Setup UART communication on an Arduino
void setup() {
  Serial.begin(9600);  // Start UART communication at 9600 baud rate
}

void loop() {
  Serial.println("Hello, World!");  // Send "Hello, World!" over serial
  delay(1000);
}

2. SPI (Serial Peripheral Interface)

SPI is a synchronous serial communication protocol that uses a master-slave architecture. It relies on a clock signal to ensure data is transferred in sync between the devices. It is commonly used in applications where high data rates and multiple devices are involved, such as SD cards, sensors, and displays.

Key Features of SPI:

Example SPI Code (Arduino):


#include 

void setup() {
  SPI.begin();  // Initialize SPI
}

void loop() {
  digitalWrite(SS, LOW);  // Select the slave device
  SPI.transfer(0xAA);     // Send a byte over SPI
  digitalWrite(SS, HIGH); // Deselect the slave device
  delay(1000);
}

3. I2C (Inter-Integrated Circuit)

I2C is another synchronous communication protocol, but unlike SPI, it uses only two lines: SDA (data) and SCL (clock). I2C is commonly used for communication between microcontrollers and peripherals like EEPROMs, ADCs, and sensors.

Key Features of I2C:

Example I2C Code (Arduino):


#include 

void setup() {
  Wire.begin();  // Initialize I2C
}

void loop() {
  Wire.beginTransmission(8);  // Start communication with device at address 8
  Wire.write("Hello!");       // Send data
  Wire.endTransmission();     // Stop communication
  delay(1000);
}

4. RS-232 and RS-485

RS-232 and RS-485 are standards for serial communication that define electrical characteristics and signaling. RS-232 is commonly used for short-distance communication between computers and devices, while RS-485 supports longer distances and multiple devices on the same bus.

Key Features:

5. USB (Universal Serial Bus)

USB is the most common serial protocol used today, allowing high-speed data transfer between computers and peripherals. It supports different data rates, from low-speed (1.5 Mbps) to high-speed (480 Mbps) and even SuperSpeed (up to 5 Gbps).

Key Features of USB:

6. CAN Bus (Controller Area Network)

CAN Bus is a robust serial communication protocol used primarily in automotive and industrial applications. It allows microcontrollers and devices to communicate with each other without needing a host computer. CAN Bus is ideal for environments that require reliability and real-time communication.

Key Features of CAN Bus: