I have successfully implemented an initial I2C bus (I2C1) in my custom board design (using STM32F405). I then added a second I2C bus (I2C2) to my design and have initiated it and set it up identical to I2C1. The first bus continues to operate correctly (sending a clock signal out at 100 kHz). I've specified the same clock frequency for the second bus. However the SCL pin only puts out a *constant* 60 Hz square wave. What could I be doing wrong?