Conflict between ic2-bus and GPIO pins?

[daw87uk]

Hi

I have a Pi 3 controlling GPIO pins and also IO PI expander.

It's been working fine but now there are problems after I've been tinkering with other code. I've narrowed it down to the problem being caused by the setting of the GPIO pins.

For example, if I run the following after the Pi boots (and without running any other code)...

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echo "2" > /sys/class/gpio/export
echo "out" > /sys/class/gpio/gpio2/direction
echo "3" > /sys/class/gpio/export
echo "out" > /sys/class/gpio/gpio3/direction

...then I get the following error when running a test script for the IO PI expander, even though there's no apparent connection (physical or otherwise) between those GPIO pins and the IO PI expander:

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Failed to import IOPi from python system path
Importing from parent folder instead
Traceback (most recent call last):
  File "ht1.py", line 111, in <module>
    main()
  File "ht1.py", line 44, in main
    iobus2 = IOPi(0x21)
  File "../IOPi.py", line 117, in __init__
    self.__ioaddress, self.IOCON, self.__ioconfig)
IOError: [Errno 5] Input/output error

Does anyone know why the setting of the GPIO pins would upset the ic2-bus?

Thanks.

[ghp]

Hello, not sure what this "IO PI expander" is, but possibly a MCP23017 driven by I2C-signals. These I2C-signals are usually provided by GPIO-2, GPIO-3 . Setting these pins to specific directions could conflict with the I2C driver.
Do you have a link to this product (including schematic ?)

[daw87uk]

Thanks for your reply.

You're right - I recently added pins 2 & 3 to what I was doing and that created a conflict, as things worked again when I removed them from the code!

For info, the IO Pi expander schematic is on this page - https://www.abelectronics.co.uk/p/54/io-pi-plus

Thanks.