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I2C Cheat Sheet (DRAFT) by

I2C cheatsheet for Python and Linux

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Basics

Slaves have addresses by which they respond, address might be config­urable
Master requests data from slaves or sends data to them, slaves answer
SDA/SCL wired in parallel, each connected to 3.3V through a resistor (called pullup resistor)
Resistor is needed because lines can only be made low, neither master nor slave can make a line high
No need to use Python GPIO functions because there's a separate Raspberry Pi block able to speak I2C which we can use to commun­icate in I2C language

I2C bus connection

I2C signal

Registers

Reading and writing

 

Errors

 
 

Usage

Commun­ication between microc­ont­rollers
Getting data from sensors
Readin­g/w­riting memory chips
Adding GPIO to your project
Config­uring I2C-en­abled devices

i2cdetect

Call "i2cdetect -y bus_num" in command line to scan for devices:
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- 27 -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- UU
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- -- 
Hexadecimal number means that device responded. UU means this address is taken by the Linux kernel.

I2C buses and bus numbers

Do "ls /dev/i2c*" in command-line to list available I2C buses (separate I2C lines, Raspberry Pi has 1 available). /dev/i2c-1 means bus number 1.
Most likely, bus number will be 1, but check anyway.

CLI utilities for readin­g&­writing I2C

#Read a byte from I2C device:
i2cget -y bus_num dev_addr register # If unsure, leave register at 0
#Write a byte to I2C device:
i2cget -y bus_num dev_addr register byte_value
#Dump all registers of I2C device:
!!!!!!!!!!!i2cfump -y bus_num dev_addr register byte_value

Debugging problems

Check that the I2C driver has been loaded: "sudo modprobe i2c-de­v".