Resolved! F4 and F7 SPI CLK waveform
During testing an SPI DAC (TI DAC8563) on an STM32F446RE (where it works) and on an STM32F767ZI (where output is always 0V), I noticed a different SPI clock waveform.In F4 you have three "8 pulses" signals from CLK (the message from MOSI is 24 bit), ...