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Although I2C has been open source since 2006 there is a fee charged for obtaining a slave address from NXP. In real life this large collection of devices is never used, it is rare to see over a dozen I2C devices on one bus.Ī newer, 10-bit addressing scheme has been implemented, it is backward-compatible with the existing 7-bit addressing method.Ĭommercial I2C devices are allocated I2C address by NXP, who maintain the bus specifications. They use a 7-bit addressing scheme, so up to 128 slaves can be on one I2C bus. Slave devices do have an address, and this address needs to be unique on the bus. The master devices do not have an address assigned to them. There can be more than one master device on the bus but only one can be the active master at any given moment. It requests data from the slaves individually. The Master device controls the bus and supplies the clock signal. There are two types of devices that can be interfaced to the I2C bus – Masters and Slaves.

#WIRE.H LIBRARY ARDUINO DOWNLOAD HOW TO#

We will discuss this more in a future article when I show you how to interface a Raspberry Pi (3.3-volt logic) with an Arduino Uno (5-volt logic). This difference in supply voltages can cause issues when you are interfacing I2C devices that use different logic levels. It can also be a lower voltage for some high-speed I2C implementations. Note that the supply voltage is not standard, it can be either 3.3 or 5-volts. There are two pull-up resistors attached to each signal line, they pull the bus up to the supply voltage when it is inactive. SDA – This is the bidirectional data line.

How I2C WorksĪn I2C bus has two signals, along with a power and ground connection. On an I2C bus it is the master that determines the clock speed.

Ultra Fast Mode – Maximum clock frequency of 5 MHz.

Hi-Speed Mode – A maximum clock frequency fo 3.4 MHz.

Fast Mode – This has a maximum clock speed of 400 KHz.

Most common applications still use this speed, as it is quite sufficient for transferring data from sensors and to simple displays. The original I2C bus had a maximum speed of 100 KHz. The maximum distance of reliable transmission decreases as the speed increases, at the slowest speed (100 Kbaud or a clock rate of 100 KHz) the maximum distance is about a metre. I2C can only be used over short distances, after all, it was originally meant to communicate between integrated circuits on the same printed circuit board. It is not particularly fast, although for most of its intended uses it is plenty fast enough. I2C does have several limitations however. Many displays and sensors interface to their host controller using I2C. I2C is used with microcontrollers like the Arduino and with microcomputers like the Raspberry Pi. It is also called “IIC” or ‘I squared C”. I2C is an abbreviation for “Inter-Integrated Circuit”. Times have changed, Phillips is now NXP and I2C has become a communication standard that is supported by virtually every major semiconductor manufacturer. It was originally developed by Phillips in 1982 to allow integrated circuits within television receivers to communicate with one another.

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I2C is a serial protocol used on a low-speed 2-wire interface. In future articles we will see how we can build our own I2C devices, how to interface a Raspberry Pi and an Arduino using I2C and how to do some advanced I2C configurations, including using multiple masters on one I2C bus. This will be the first of four articles on I2C. We’ll also see how it can be used to exchange information between two Arduinos and how it can be used to allows one Arduino to control another one. Today we will correct that and learn more about I2C. Although we have used many I2C sensors and displays in previous articles we have not actually looked into how I2C works and how it can be used to communicate between microcontrollers.

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