How to manage the I2C buses on CM Panels

This article illustrates how to use the I2C busses on the CM-Panels

The I2C bus is used in the following ways on the two model of CM Panel available:

CM-Panel BASIC
- Generic BUS on EXP1 connector
- Generic BUS on EXP2 connector
- Raspberry cam criptochip
CM-Panel POE
- Real Time Clock chip
- Acme sensor port
- Groove Seedstudio port
- QWIIC port
- Raspberry cam criptochip

I2C on EXP1 and EXP2 connectors onc CM-Panel BASIC

On the EXP1 and EXP2 connector of CM-Panel BASIC there are two I2C ports available for the user application

EXP1 pin	Signal	Line
11	I2C SDA1	GPIO 44
13	I2C SCL1	GPIO 45
16	GND

EXP2 pin	Signal	Line
15	I2C SDA0	GPIO 28
13	I2C SCL0	GPIO 29
16	GND

Enable the I2C ports

By default on the CM-Panel BASIC the I2C bus 1, available on GPIO 44 and 45 lines, is enabled just at Kernel level to comunicate with the touch panel and camera crypto chip.

This is done by modify the standard file config.txt as explained here:

The line used in the /boot/config.txt file is this:

dtoverlay=i2c1,pins_44_45

this setting is sufficient to enable I2C at the kernel call level. If you want to access I2C also from normal applications launched in user space, you need to enable the driver using the utility:

$ sudo raspi-config

and enable the port by following these options:

Interface Options -> I2C -> Would you like the ARM I2C interface to be enabled? YES

then reboot.

Install the i2c-tools to check the I2C bus from user space.

$ sudo apt update
$ sudo apt install i2c-tools

Type:

$ sudo i2cdetect -l

to see the logical devices to use in out applications

i2c-1   i2c         bcm2835 (i2c@7e804000)              I2C adapter

Type:

$ sudo i2cdetect -y 1

Result on CM-Panel BASIC will be:

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

Result on CM-Panel POE will be:

     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:                         -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- UU -- -- 
50: -- -- -- -- -- -- -- -- -- -- -- -- -- UU -- -- 
60: -- -- -- -- -- -- -- -- 68 -- -- -- -- -- -- -- 
70: -- -- -- -- -- -- -- --

The "UU" character displayed instead of the I2C address means that the chip is managed directly by a Kernel driver.