{"id":61842,"date":"2025-06-10T15:26:01","date_gmt":"2025-06-10T19:26:01","guid":{"rendered":"https:\/\/www.engineersgarage.com\/?p=61842"},"modified":"2025-06-11T12:15:56","modified_gmt":"2025-06-11T16:15:56","slug":"articles-raspberry-pi-i2c-protocol","status":"publish","type":"post","link":"https:\/\/www.engineersgarage.com\/articles-raspberry-pi-i2c-protocol\/","title":{"rendered":"RPi Python Programming 24: I2C explained"},"content":{"rendered":"

In the previous tutorial<\/strong><\/a>, we covered how to interface a NEO-6M GPS module with Raspberry Pi (RPi). The module communicates with RPi over the universal asynchronous receiver\/transmitter or\u00a0<\/span>UART protocol<\/a><\/strong>.\u00a0<\/span><\/p>\n

The UART is the most common point-to-point data communication protocol. But, it\u2019s not the only serial communication protocol. In embedded electronics, I2C and SPI protocols are also widely used for serial data communication. Unlike UART, I2C and SPI are master-slave-type synchronous serial data standards.\u00a0<\/span><\/p>\n

In this tutorial, we\u2019ll discuss the basics of the I2C protocol.\u00a0<\/span><\/p>\n

What is an I2C?\u00a0<\/span><\/strong>
\n<\/span>An inter-integrated circuit (I2C) or two-wire interface (TWI) is a synchronous serial protocol originally developed by Philips Semiconductors (now NXP). It\u2019s a multi-master, multi-slave serial bus for low-speed devices that only requires two wires for serial data communication between multiple devices. It can easily be implemented with two digital input\/output channels on a device.<\/span><\/p>\n

An I2C bus has just two wires over which hundreds of devices can communicate serial data.\u00a0<\/span><\/p>\n

As a master-slave type communication standard, at least one device connected to the bus should be the master. It\u2019s the master device that generates a clock signal for synchronous serial communication.<\/span><\/p>\n

The slave devices can transfer data to and from the master device(s), which access slave devices by their I2C addresses. The address of each slave device on an I2C bus must be unique. However, the I2C slave devices still must obtain their addresses from NXP.\u00a0<\/span><\/p>\n

There are only two wires in I2C where devices can be connected:<\/span><\/p>\n

1.<\/strong> Serial data (SDA) \u2013 the line over which the master and slave devices communicate serial data
\n<\/span>2.<\/strong> Serial clock (SCK) \u2013 the line over which master device(s) generate the clock signal.\u00a0<\/span><\/p>\n

The I2C is a half-duplex type of communication. Note: a master device can only read or write data to the slave at one time. Also, the clock signal and the read and write operations are all controlled by the master device(s).\u00a0<\/span><\/p>\n

Although there can be an unlimited number of master devices connected to the I2C bus, the maximum number of slave devices can be 112 (in 7-bit addressing) or 1008 (in 10-bit addressing).\u00a0<\/span><\/p>\n

The I2C bus drivers are open drain, which means the devices can pull the I2C signal line low but cannot drive it high. By default, both the lines are pulled high by pull-up resistors until the bus is accessed by a master device. This is useful to avoid bus contention.\u00a0<\/span><\/p>\n

Since master devices can only pull the signal line low, there can be no conflict between multiple masters \u2014 such as one master pulling the line low while the other drives it high. If at any time, the signal line is low, it means it\u2019s in access to a master device.\u00a0<\/span><\/p>\n

Therefore, only one master can access the I2C bus at a time. And the bus master can only read or write data with one slave at a time.<\/span><\/p>\n

\"\"<\/a><\/p>\n

The serial data communicated over the I2C is split into 8-bit data packets. The data transfer rate depends on the clock frequency. In the standard mode, the clock frequency is 100 to 400 kHz.\u00a0<\/span><\/p>\n

The clock frequency is:\u00a0<\/span><\/p>\n