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I have a Raspberry Pi 4 B and I'm trying to set up in I2C Connection with an MCP23018-E/SP I/O-Port-Expander via GPIO02 and GPIO03. I have enabled I2c on the Raspi by:

  • adding: dtparam=i2c1=on to /boot/config.txt

            dtparam=i2s=on      to    /boot/config.txt
    
            dtparam=i2c_arm=on  to    /boot/config.txt 
    
            dtoverlay=i2c1,pin2_3(tried it as well without the last three)
    
  • added all modules in /etc/modules

  • enabled automatic load of i2c kernel at boot

  • installed i2c-tools, python-smbus.

for
$ ls -l /dev/i2c-*
I get:
crw-rw--- 1 root i2c 89, 0 Okt 05 18:00 /dev/i2c-1

So my bus should be set up correctly. I know, you have to use the alternative functions for the GPIO Pins to get I2C, so I set:

  • raspi-gpio set 02 a0
  • raspi-gpio set 03 a0 (because SDA1/SCL1 are Alternate functions for GPIO 02 and GPIO 03. I get as well for raspi-gpio get 02,03 that the SDA/SCL are enabled.

I tried it aswell for different Pins, whose alternate function can provide an i2c buses, but none of them show a result for i2cdetect -y 1

I looked at the channels with an oscilloscope, and from my point of view, the Raspi is NOT sending SDA and SCL, there are both just high at 3,3 V.

I really tried everything to send the I2C signals, but it will not work and I don't have a different device to check my circuit, but I'm pretty sure on the hardware side everything is correctly wired.

Any help would be really helpful.

PJ_2810

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Most of what you have configured is not needed and may be part of the problem.

Don't add modules to /etc/modules, don't set the GPIO mode with raspi-gpio or similar, don't enable automatic load of I2C kernel at boot.

Remove everything you have done and just add the following line to /boot/config.txt.

dtparam=i2c_arm=on

Reboot and check that the device /dev/i2c-1 exists. If it does you are ready to go.

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