There are many models of STM32 microcontroller, and the package is also very complicated, each model, each package, the SCL and SDA pin positions of its I2C bus are different, and the definition of the pin is also divided into 'default reuse function position' and 'redefine function position'. The specific location can only refer to the data manual of each single chip microcomputer model.
Taking LQFP100 package STM32F103 as an example, it has two I2C buses, of which 1 channel SCL default at 92 pin, can be redefined at 95 pin; SDA is on pin 93 by default and can be redefined on pin 96.