I have a brand new Grove - I2C Motor Driver V1.3 + Grove Base Hat for Raspberry Pi.
When connecting the Motor driver to i2c of the base hat it immediately jams all i2c communication: all i2c devices that are perfectly running before stop working when the motor driver is attached. In addition “i2cdetect” runs slowly and doesn’t find any i2c device (before attaching the motor driver “i2cdetect” detects the other i2c devices).
Even if the motor driver is the only attached i2c device “i2cdetect” runs slowly and doesn’t find any i2c device.
In addition all 4 trning direction leds (2 x red, 2 x green) on the motor driver are always on as soon as power is attached. Resetting the device is not helping.
Same issue when connecting the same motor driver to the XIAO RA4M1: four LEDs on, slow and no detection, cannot say for multiple I2C devices (the Grove shield for this microcontroller only has one I2C port).
Still the motor driver is correctly detected on an Arduino UNO R3.
Sounds to me like, When you connect multiple I2C devices to a single bus, the communication speed often slows down because the increased number of devices significantly raises the bus capacitance, leading to slower signal rise times and ultimately limiting the maximum data transfer rate on the bus
Cable length, or contention for two type of devices can play a role in it too.
You can try and Reduce the Length of the connections or use /change the Pull up resistor values to clean it up. Or add signal buffers to improve it.
PJ 