after enabling I2C1 [I2C_GenerateSTART(I2C1, ENABLE);] on some (not all, 3 from 12) of my PCBs the I2C_EVENT_MASTER_MODE_SELECT isn't generated. Do you know any Hardware-Bug/Issue using I2C1? The other PCBs with the same devices and software working properly! I'm using the STM32F103RBT6 Cortex-M3.