An In-Depth Exploration of I2C Protocol in Modern Embedded Systems.

I2C bus protocol uses two lines (SDA and SCL) for communication with multiple devices, while SPI typically uses four lines (MOSI, MISO, SCK, and SS). I2C has built-in addressing and supports multiple masters, making it simpler to wire but slower (100kHz-400kHz standard speeds). SPI is faster (several MHz) but requires additional chip select lines for each device. For IoT applications, I2C communication protocol is often preferred when connecting multiple sensors due to its simpler wiring, while SPI is chosen when higher data rates are needed, like for displays or storage.

I2C interface can theoretically support up to 127 devices with 7-bit addressing or 1023 devices with 10-bit addressing. However, in practical IoT applications, the limit is usually lower due to:

• Bus capacitance (limited to about 400pF)
• Power requirements
• Address conflicts (many I2C devices use fixed addresses)
• Signal integrity considerations For most IoT applications, 8-12 devices are a practical limit without using multiplexers or bus buffers.

I2C communication protocol requires pull-up resistors on both SDA and SCL lines because it uses open-drain/open-collector outputs. The resistor values are critical and depend on:

• Bus capacitance
• Operating voltage
• communication speed

Typical values:

• For 3.3V systems: 2.2kΩ to 10kΩ
• For 5V systems: 1.8kΩ to 4.7kΩ

Too low value wastes power, while too high value make communication unreliable. For IoT devices, this is crucial for power consumption and reliability.

The I2C bus protocol was designed for short-distance communication on a single PCB. Practical limits:

• Standard I2C bus communication: typically reliable up to 50cm
• With special considerations (buffers, lower speeds): up to 2-3 meters
• Limitations are due to:
• Capacitance (400pF max)
• Signal integrity
• EMI susceptibility
• For longer distances in IoT applications, solutions include:
• I2C buffers/repeaters
• Converting to differential signaling
• Using alternative protocols like RS-485 for long distances