I2C Addresses and Troublesome Chips

I2C Addresses and Troublesome Chips

I2C addresses from 0x00 to 0x7F (inclusive). Flaky I2C devices.

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by lady ada and
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published July 29, 2017, last edited January 22, 2025
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Overview

When people need to communicate with each other, we use language. If two people speak the same language, they can talk all they want about all sorts of topics. If they don't speak the same language, communication is difficult. Likewise, electronic parts need to communicate - and they also have their own languages. There are a few common languages that are spoken. The most popular ones are TTL Serial, SPI, I2C, I2S, 1-Wire, and Parallel (such as 8080 or 6800). Of these, Parallel and SPI can 'share a bus' using a select line - multiple devices can share the pins as long as they have a single pin that can be used to indicate who is permitted to speak at one time. 1-Wire and I2C are true shared-bus protocols - you can have 100+ components all talking at once using the same 2 wires (for I2C) or 1-wire (for the aptly-named 1-wire). 1-Wire is much slower than I2C and is a strongly-patented protocol owned by Maxim so you won't see a lot of devices out there other than Maxim/Dallas parts that use 1-wire.

I2C - Inter-Integrated Circuit communications!

This guide doesn't cover the nitty-gritty details of I2C, other than to note that you can connect multiple I2C devices (often referred to as "I2C peripheral") to a single I2C controller (a.k.a "I2C main") using only two wires.

For example, in this diagram, one Metro (e.g. Arduino compatible) connects to 5 devices.

In general, you can only have one controller and up to 127 devices. (There are exceptions such as multi-main and 10-bit address devices but they are so rare and we've never seen them in practice)

I2C is incredibly popular because it uses only 2 wires, and like we said, multiple devices can share those wires, making it a great way to connect tons of sensors, drivers, expanders, without using all the microcontroller pins. The only bad news about I2C is that each I2C device must have a unique address - and the addresses only range from 0 to 127 (aka 0 to 0x7F hex). One thing this means is that if you have two accelerometers (lets say) and they both have address 0x22 you cannot have both of them on the same I2C lines.

There are a few work-arounds:

  • One is you might be able to power down or 'de-select' one sensor or another at a time.
  • Another is that some boards have an address-select line or jumper or other configuration. If you can set one to a different address you're good to go.
  • Some devices have a software-reprogrammable address, where they come up as one address on boot but can be told to change address. Oftentimes, the new address is forgotten on reboots, so you have to de-power all the other similarly-addressed devices while you do so.
  • You can use an I2C multiplexer like the TCA9548A which will let you use one I2C address to talk to the multiplexer and tell it which line you want to enable

Since we deal with so many I2C devices we thought it would be handy to have a table with all the most common sensors and modules we encounter, and their I2C address!

Continue onto the next page to see our current list

Page last edited March 08, 2024

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The List

OMG Can you believe it? We didn't include every I2C device in the known universe! Fear not, you can now submit a pull request on GitHub to add your favorite device! Visit https://github.com/adafruit/I2C_Addresses/ for more information.
All I2C addresses here are in 7-bit format

Special cases:

  • PCA9685 can use any address between 0x40 to 0x7F. Some of these addresses are fixed. See the datasheet for details. This chip is used in:
    • PWM/Servo Breakout
    • PWM/Servo Shield
    • PWM/Servo HAT
    • PWM/Servo Bonnet
    • PWM/Servo Wing
    • DC & Stepper Motor Shield
    • DC & Stepper Motor HAT
    • DC & Stepper Motor Bonnet
    • DC & Stepper Motor Wing
  • 0x00 - 0x07 and 0x78 - 0x7F are reserved I2C addresses

0x00 - 0x0F

0x00

  • Reserved - general call address

0x01

  • Reserved for CBUS compatibility

0x02

  • Reserved for I2C-compatible bus variants

0x03

  • Reserved for future use

0x04

  • Reserved for HS-mode controller

0x05

  • Reserved for HS-mode controller

0x06

  • Reserved for HS-mode controller

0x07

  • Reserved for HS-mode controller

0x0B

0x0C

0x0D

0x0E

0x0F

0x10 - 0x1F

0x10

0x11

0x12

0x13

0x14

0x18

0x19

0x1A

0x1B

0x1C

0x1D

0x1E

0x1F

0x20 - 0x2F

0x20

0x21

0x22

0x23

0x24

0x25

0x26

0x27

0x28

0x29

0x2A

0x2B

0x2C

0x2D

0x2E

0x30 - 0x3F

0x30

0x31

0x32

0x33

0x34

0x35

0x36

0x37

0x38

0x39

0x3A

0x3B

0x3C

All OLED controllers below use either 0x3C or 0x3D depending on a control pin. Hardware selectable on some displays with a solder jumper.

0x3D

All OLED controllers below use either 0x3C or 0x3D depending on a control pin. Hardware selectable on some displays with a solder jumper.

0x3E

0x3F

0x40 - 0x4F

  • PCA9685. See "Special Cases"

0x40

0x41

0x42

0x43

0x44

0x45

0x46

0x47

0x48

0x49

0x4A

0x4B

0x4C

0x4D

0x4E

0x4F

0x50 - 0x5F

  • 24LCxx series EEPROMs of various sizes and makes. Example: PC Monitor's EDID (0x50)
  • PCA9685. See "Special Cases"

0x50

0x51

0x52

0x54

0x55

0x56

0x57

  • MB85RC FRAM (0x50 - 0x57)
  • MAX3010x Pulse & Oximetry Sensor (0x57)

0x58

0x59

0x5A

0x5B

0x5C

0x5D

0x5E

0x5F

0x60 - 0x6F

  • PCA9685. See "Special Cases"

0x60

0x61

0x62

0x63

0x64

0x65

0x66

0x67

0x68

This address is really popular with real time clocks, almost all of them use 0x68!

0x69

0x6A

0x6B

0x70 - 0x7F

  • PCA9685 Shields, HATs, Breakouts, Wings etc - See "Special Cases"

0x70

0x71

0x72

0x73

0x74

0x75

0x76

0x77

0x78

  • Reserved for 10-bit I2C addressing

0x79

  • Reserved for 10-bit I2C addressing

0x7A

  • Reserved for 10-bit I2C addressing

0x7B

  • Reserved for 10-bit I2C addressing

0x7C

  • Reserved for future purposes

0x7D

  • Reserved for future purposes

0x7E

  • Reserved for future purposes

0x7F

  • Reserved for Future Purposes

Page last edited March 08, 2024

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Troublesome Chips

Troublesome chips:

Some sensors or chips have non-standard behavior that causes issues when trying to use I2C. Here's a few of the ones to watch for

  • AGS20MA - Use a bus speed of 20-30 kHz.
  • AM2320 - Automatic sleep behavior causes unreliable scanning.
  • ATECCx08 - Use slow-speed I2C to get out of sleep mode.
  • BNO055 - Uses clock stretching, violates I2C protocol timing in some cases, and sometimes needs to be reset. Does not work well on i.MX RT10xx chips. Does not work well with ESP32, ESP32-S3 before ESP-IDF 5.3.2. Use CircuitPython 9.2.2 or later.
  • BNO085 - Uses clock stretching, violates I2C protocol timing in some cases, and sometimes needs to be reset. Does not work well on i.MX RT10xx chips, ESP32, ESP32-S3.
  • CCS811 - Uses clock stretching.
  • LC709203F - Repeated start, clock stretching, sleep mode
  • MCP9600 (date codes 1845 or before) - bug: duplicate data from register. reads, perhaps due to clock stretching.
  • MCP9600, MCP9601 - Repeated start, clock stretching. Often will not respond to zero-length writes, so scanning the I2C bus to find the device can fail.
  • PN532 - Clock stretching.

If you're using Raspberry Pi with these chips, check out our guide on how to work-around clock stretching.

Troublesome microcontrollers:

  • MicroChip Atmel SAMD21, SAMx5x - I2C bus frequency below 95 kHz not available in CircuitPython when I2CTarget is drive with a 48 MHz clock, which is typical. CircuitPython checks for out-of-range bus frequencies.

  • Espressif ESP32-S3 - Use software that uses Espressif ESP-IDF v5.3.2 or later. When using versions of the Espressif ESP-IDF SDK older than v5.3.2, ESP32-S3 has problems with I2C devices that do clock stretching or have other unusual timing behavior. ESP-IDF is the underlying software used by CircuitPython and the Arduino esp32 board support package. CircuitPython 9.2.2 and later use ESP-IDF 5.3.2 and later. Arduino esp32 v3.2.0 and later use ESP-IDF v5.4.0 and later. These versions support most I2C devices well. However, some of the troublesome chips listed above still don't work well or at all even with ESP-IDF v5.

Page last edited March 08, 2024

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