I2C

Connects Components To Microcontrollers Inside Devices

I2C (Inter-Integrated Circuit, aka IIC, Speak: Eye-Squared-See) is a synchronous bus system invented 1982 by Philips. Today, it is widely used to connect components to microcontrollers inside devices.

Since I2C is relatively slow, for components requiring higher data rates (such as color displays), SPI is used.

Quick Overview

I2C is a bus that is used to inter-connect components inside a device and over a short distance.

Here are its key benefits:

  • GPIOs: requires just two GPIOs to connect up to 127 devices (SDA and SCL)
  • Device Address: every device on the bus has a unique predefined address

And these are the most important limitations:

  • Speed: in standard mode, speed is 100 kbit/s. There are faster modes (400 kbit/s, 1/3.4/5 MBit/s) that are not supported by all devices.
  • Noise: Its high impedance and low noise immunity require a common ground and short distances.
  • Address: Since addresses are often not fully configurable or even fixed, the already small 7-bit address space is further limited,effectively preventing the use of multiple components of the same kind (i.e. multi-display use cases).

Buffers and multiplexers can stretch the limits of I2C. Most of the time, switchting to a different bus system that is suited for the task (i.e. SPI) is a better approach.

I2C Address

I2C uses a 7-bit address to uniquely address invididual devices. Theoretically, this provides 127 unique device addresses.

Realistically, most components have fixed addresses or just a small number of selectable addresses. So the number of I2C devices on an I2C bus is much lower.

Hex vs. Binary vs. Decimal

I2C addresses can be specified in different formats.

  • in binary format, the address bits are specified, i.e. 1000000. The true address is defined by two 4-bit values: 0100 0000. In this example, these would be the numbers 4 and 0, resulting in the I2C address 40.
  • in hexadecimal format, the address is specified as 0x40
  • in decimal format, the hexadecimal address is converted to the decimal system: 0x40 can also be expressed as 60.

The most commonly used format are hexadecimal addresses.

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(content created Jul 07, 2024)