raspberry2c

Software implementation for I2C communication between AVR microcontrollers and a Raspberry PI.

Supported MCUs

The I2C software implementation has definitions for the following MCUs:

• ATTiny2313
• ATTiny24
• ATTiny24A
• ATTiny25
• ATTiny26
• ATTiny261
• ATTiny44
• ATTiny44A
• ATTiny45
• ATTiny461
• ATTiny84
• ATTiny861
• ATMega165
• ATMega169
• ATMega325
• ATMega3250
• ATMega329
• ATMega3290
• ATMega645
• ATMega6450

Prepare the Raspberry PI for I2C communication

Activate I2C kernel module

Edit the file /etc/modprobe.d/raspi-blacklist.conf

$ sudo vi /etc/modprobe.d/raspi-blacklist.conf

Search for the row

blacklist i2c-bcm2708

and comment it

#blacklist i2c-bcm2708

Leave the editor (with :wq!)

Load I2C kernel modules

Load the required kernel modules

$ modprobe i2c-bcm2708
$ modprobe i2c_dev

Use lsmod to check, if the modules are loaded.

$ lsmod
Module                  Size  Used by
nfsd                  236425  11
i2c_dev                 5587  20
i2c_bcm2708             3542  0
snd_bcm2835            19889  0
snd_pcm                74834  1 snd_bcm2835
snd_seq                52536  0
snd_timer              19698  2 snd_seq,snd_pcm
snd_seq_device          6300  1 snd_seq
snd                    52489  5 snd_seq_device,snd_timer,snd_seq,snd_pcm,snd_bcm2835
snd_page_alloc          4951  1 snd_pcm

To load the modules automatically on boot, you can add them to the /etc/modules file.

$ sudo vi /etc/modules

snd_bcm2835
i2c-bcm2708
i2c-dev

Install and use I2C tools

Install the i2c-tools

$ sudo apt-get install i2c-tools

Add your user to the i2c usergroup so you don't need to use sudo to interact with the i2c device.

$ sudo usermod -aG i2c pi

Scan I2C-bus 0 for devices

$ i2cdetect -y 0

    0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- 1a -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --

Read I2C register from address 0x1a

$ i2cdump -y 0 0x1a

No size specified (using byte-data access)
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f    0123456789abcdef
00: ff c7 16 58 0e 0f 10 11 12 13 00 00 00 00 00 00    .??X??????......
10: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
20: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
30: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
40: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
50: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
60: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
70: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
90: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
a0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
b0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
c0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
d0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
e0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
f0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................

Write 0xff into I2C register 0x00 at address 0x1a

$ i2cset -y 0 0x1a 0x00 0xff

Schematics

Raspberry GPIO Pins

see http://elinux.org/RPi_Low-level_peripherals#General_Purpose_Input.2FOutput_.28GPIO.29