In the manual P 263:
Bits 27:24 MCOSEL[3:0]: Microcontroller clock output
Set and cleared by software.
0000: MCO output disabled, no clock on MCO
0001: SYSCLK system clock selected
0010: MSI clock selected.
0011: HSI16 clock selected.
0100: HSE clock selected
0101: Main PLL clock selected
0110: LSI clock selected
0111: LSE clock selected
1000: Internal HSI48 clock selected
But the real order is
0000: MCO output disabled, no clock on MCO
0001: LSE clock selected
0010: LSI clock selected
0011: HSE clock selected
0100: HSI16 clock selected.
0101: Main PLL clock selected
0110: SYSCLK system clock selected
0111: MSI clock selected.
1000: HSI48 clock selected
This is the order in the CubeMX mux setting for the MCO output.
