I2C
This page will summarize the informations to use the I2C bus on our boards.
Contents
Overview
The I2C bus is a simple & widely used two wires synchronous bus. It has been developped by Philips (now NXP).
The standard frequency is 100kHz but 400kHz devices can be found (for example on the i.MX).
Single and multi masters are supported. Only the single master configuration will be discussed here.
The bus is based on two signals: SDA and SCL.
- SDA: bidirectional line for data
- SCL: unidirectional line for the clock (provided by the master)
Details can be found in the specification here.
Linux configuration
By default the I2C bus is activated in the Armadeus distrib. If you need to deactivate it, take a look at the linux menuconfig:
$ make linux-menuconfig
Linux user space C code
Kernel source has a good documentation on using i2c bus through /dev with C program, it can be found in kernel source directory Documentation/i2c/dev-interface.
You can find a sample code under target/packages/ch7024ctrl/ of the Armadeus distribution ( or here through SF's SVN browsing )
On OPOS6UL
By default, OPOS6UL kernel and rootfs are compiled with lm-sensors tools. There are 2 i2c busses on the opos6ul numeroted 1 and 2 on schematics and 0,1 under Linux. The i2c busses can be listed with command i2cdetect:
# i2cdetect -l
i2c-1 i2c 21a4000.i2c I2C adapter
i2c-0 i2c 21a0000.i2c I2C adapter
The second bus (I2C2) is available on the RaspberryPi connector.
Detect
To see devices connected on one of the i2c master, use the command i2cdetect with the bus number:
# i2cdetect 1
WARNING! This program can confuse your I2C bus, cause data loss and worse!
I will probe file /dev/i2c-1.
I will probe address range 0x03-0x77.
Continue? [Y/n]
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: 40 -- 42 43 -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: 60 -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --
In this bus we can see 4 devices in addresses 0x40, 0x42, 0x43 and 0x60
On APF27
Tested I2C chips
- RTC: DS1327
- DAC: Max5821
- Video: CH7024 AD9889 & TFP410
- Misc: WM8311
- EEPROM:
APF27 I2C chips
List of all hardware devices on APF27 I2C busses
- "I2C" and "I2C2" are the busses names from the iMX27 datasheet
- "I2C-0" and "I2C-1" are the corresponding linux device names
- I2C (I2C-0):
none
- I2C2 (I2C-1):
24AA02 Microchip Technology
256X8 EEPROM
I2C ADDRESS 0x50 to 0x57 (bits 0-2 are don't care)
APF27_DEV I2C chips
List of all hardware devices on APF27_DEV I2C busses
- "I2C" and "I2C2" are the busses names from the iMX27 datasheet
- "I2C-0" and "I2C-1" are the corresponding linux device names
- I2C (I2C-0):
DS1374 Dallas Semiconductors
32 bits time of day counter (1s increment)
I2C ADDRESS 0x68
MAX5821L MAXIM
Dual 10bits DAC
I2C ADDRESS 0x38
- I2C2 (I2C-1):
AD9889 Analog Devices
HDMI I/F
I2C ADDRESSES
* Main ctrl register 0x39
* Spare packet memory (31 bytes) 0x38 (default)
* EDID memory area (256 bytes) 0x3F (default)
I2C bus logic 5v level adaptation (if necessary)
if you want to use I2C devices which can not work with the I2C voltage of the APF board, a level translator has to be used, for example a PCA9306 from NXP:
- Connect pin 1 to the local GND
- Connect pin 2 to the local I2C iMX supply voltage
- Connect pin 3 to the SCL output of the APF
- Connect pin 4 to the SDA input/ouput of the APF
- Connect pin 7 and 8 together and the add a 200K resistor in parallel to a 100nF capacitor to GND
- Connect a pullup of 1.7K between your I2C device supply and the SCL line (pin 6)
- Connect a pullup of 1.7K between your I2C device supply and and the SDA line (pin 5)
For more details, take a look at the PCA9306 datasheet. This chip is the one that can be mounted by users on the APF9328DevFull board.
As a low-cost alternative, a level shifter can be built with a pair of N-channel mosfets (such as a BS170). See the Application Note 97055.
