Sharing I2C ports from 2 different PYs

[ADenislebel]

I have two I2C devices connected on the same 2 pins (port) and so far I can only run each independently with similar code for creating their own I2C object/handle. One device is a PCF8574 expander, the other is a PCA9548 multiplexer.
The code for each I2C creating is very similar.

The expander i2c init code:
from machine import I2C,Pin
Xpn_sda = Pin(10) #Pin(12) on older homstat
Xpn_scl = Pin(11) #Pin(13) on older homstat
Xpn_i2c = I2C(1,sda=Xpn_sda,scl=Xpn_scl,freq=100000)

The multiplexer i2c init code:
from machine import I2C,Pin
Mux_sda = Pin(10) # mux on i2c port0 data
Mux_scl = Pin(11) # mux on i2c port0 clock
Mux_i2c = I2C(0,sda=Mux_sda,scl=Mux_scl,freq=100000)

Both examples work independently but I want to create a single I2C driver/py that would allow them
to share the same I2C port. I'm a newbie and I don't use classes (yet) but I might have to make the jump
to get this to work. I tried simply importing the I2C object/handle from a third I2C_driver.py but that
did not work out.

My question is how do I format/create a common I2C object that can service both devices
without creating 2 objects accessing the same port. I don't believe it matters but I'm using an
RP2040 and MicroPython v1.24.1 on 2024-11-29; Raspberry Pi Pico with RP2040

[robert-hh]

You would usually create only one I2C object instance and use it for both devices. The I2C object itself does not care for which device it is used. The devices are selected by the device address.
For that you have to take the instantiation of the I2C object out of the device driver, create it separately and just supply the I2C object to the driver.

[ADenislebel]

Thank you. I will put my I2C initialization function in main.py and pass its handle to both the Xpndr.py and the Multiplx.py and give that a try. Regards Denis Lebel

…

On Fri, Sep 26, 2025 at 10:17 AM Robert Hammelrath ***@***.***> wrote: You would usually create only one I2C object instance and use it for both devices. The I2C object itself does not care for which device it is used. The devices are selected by the device address. For that you have to take the instantiation of the I2C object out of the device driver, create it separately and just supply the I2C object to the driver. — Reply to this email directly, view it on GitHub <#18143 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AEFK5ELS7A4D7SEWZ4CKHNL3UVDHDAVCNFSM6AAAAACHS5RUKCVHI2DSMVQWIX3LMV43URDJONRXK43TNFXW4Q3PNVWWK3TUHMYTINJSGI4DMMY> . You are receiving this because you authored the thread.Message ID: ***@***.*** com>

[sosi-deadeye]

First, I misunderstood the question.

Fun fact:

Yes, it's possible to have multiple I2C masters and multiple I2C slaves on the same bus, but it is not possible for two masters to act simultaneously on one slave. The I2C protocol is designed for a multi-master configuration where multiple masters can share a bus, but they must arbitrate for control. When two masters try to initiate communication at the same time, one will win arbitration and control the bus, while the other will detect it has lost and switch to slave mode, waiting to be addressed by the winning master.