Communication Protocols: I2C, SPI, UART, and CAN

Introduction

In embedded systems and IoT applications, microcontrollers and sensors need to communicate efficiently. Various communication protocols exist, each designed for specific use cases. The four most commonly used protocols are:

• I2C (Inter-Integrated Circuit): A two-wire protocol for connecting multiple devices.
• SPI (Serial Peripheral Interface): A high-speed protocol for fast data transfer.
• UART (Universal Asynchronous Receiver-Transmitter): A simple serial communication protocol.
• CAN (Controller Area Network): A robust protocol for automotive and industrial applications.

This article explores these protocols, their working principles, advantages, disadvantages, and real-world applications.

1. I2C (Inter-Integrated Circuit)

Overview

I2C is a two-wire serial protocol used for communication between multiple devices. It consists of:

• SCL (Serial Clock Line)
• SDA (Serial Data Line)

Features

• Multi-device support (master-slave architecture)
• Uses 7-bit or 10-bit addressing
• Speeds: 100 kHz (Standard), 400 kHz (Fast), 1 MHz (Fast Mode Plus), 3.4 MHz (High-Speed Mode)
• Can connect multiple sensors with minimal wiring

Advantages

✅ Supports multiple devices with only two wires
✅ Low power consumption
✅ Well-suited for sensor data transfer

Disadvantages

❌ Slower than SPI
❌ Requires pull-up resistors

Applications

• Temperature sensors (e.g., DHT11, BME280)
• EEPROM memory chips
• OLED displays

Example (I2C Communication with Espruino)

I2C1.setup({scl: D5, sda: D4});
var sensor = require("BME280").connect(I2C1);
console.log("Temperature: " + sensor.getTemperature() + "°C");

2. SPI (Serial Peripheral Interface)

Overview

SPI is a full-duplex communication protocol used for high-speed data exchange. It consists of four main signals:

• MOSI (Master Out Slave In)
• MISO (Master In Slave Out)
• SCK (Serial Clock)
• SS (Slave Select)

Features

• Single master, multiple slaves
• High-speed data transfer (up to 100 MHz in some cases)
• Full-duplex communication

Advantages

✅ Faster than I2C
✅ Supports multiple slaves
✅ Simple protocol structure

Disadvantages

❌ Requires more pins compared to I2C
❌ No built-in device addressing

Applications

• SD card modules
• TFT & OLED displays
• High-speed ADCs and DACs

Example (SPI Communication with Espruino)

SPI1.setup({mosi: D13, miso: D12, sck: D14});
var flash = require("AT25").connect(SPI1, D15);
console.log("Flash Memory ID: " + flash.read(0, 4));

3. UART (Universal Asynchronous Receiver-Transmitter)

Overview

UART is a simple serial communication protocol that does not require a clock signal. It uses:

• TX (Transmit)
• RX (Receive)

Features

• Asynchronous communication (no clock required)
• Configurable baud rate (e.g., 9600, 115200 bps)
• Full-duplex data exchange

Advantages

✅ Requires only two wires
✅ Simple and widely used
✅ No need for a master device

Disadvantages

❌ No built-in error checking
❌ Slower than SPI

Applications

• GPS modules
• Bluetooth & Wi-Fi modules
• Debugging via serial monitors

Example (UART Communication with Espruino)

Serial1.setup(9600, {tx: D1, rx: D2});
Serial1.on('data', function(data) {
  console.log("Received: " + data);
});
Serial1.write("Hello UART");

4. CAN (Controller Area Network)

Overview

CAN is a robust communication protocol designed for vehicle and industrial automation networks. It enables multiple devices to communicate without a dedicated master.

Features

• Multi-master protocol
• High noise immunity (used in harsh environments)
• Uses differential signaling (CAN_H & CAN_L)

Advantages

✅ Highly reliable and robust
✅ Works in noisy environments
✅ Multi-master support

Disadvantages

❌ More complex than UART, I2C, and SPI
❌ Requires additional transceivers

Applications

• Automotive systems (ECU communication)
• Industrial automation (robotics, PLCs)
• Medical devices

Example (CAN Communication with Espruino)

var can = require("CAN").setup({tx: D5, rx: D6, baud: 500000});
can.send([0x01, 0x02, 0x03], 0x100);
can.on("message", function(msg) {
  console.log("Received CAN message: ", msg);
});

Comparison Table

Protocol	Speed	No. of Wires	Best For
I2C	400 kHz – 3.4 MHz	2	Sensor interfacing
SPI	Up to 100 MHz	4+	High-speed devices
UART	Up to 1 Mbps	2	Simple serial data transfer
CAN	1 Mbps	2 (differential)	Automotive & Industrial

Conclusion

Each communication protocol serves different purposes.

• I2C is ideal for connecting multiple low-speed sensors.
• SPI is perfect for fast data transfer.
• UART is simple and widely used in debugging and wireless modules.
• CAN is robust and used in automotive and industrial applications.

Choosing the right protocol depends on speed, wiring complexity, and application requirements. Would you like more examples or projects on these protocols? Let us know!

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