19.4 Slow Clock

The PMC does not control the Slow clock generation. The control of the Slow clock is performed by the Supply Controller (SUPC) which embeds a slow clock generator that is supplied by the output of the power switch (VBAT or VDD3V3). As soon as the SUPC is supplied, both the 32.768 kHz crystal oscillator and the Slow RC oscillator are powered, but only the Slow RC oscillator is enabled.

MD_SLCK is always generated by the Slow RC oscillator.

TD_SLCK is generated either by the 32.768 kHz crystal oscillator or by the Slow RC oscillator.

The selection is made via the TDXTALSEL bit in the SUPC Control register (SUPC_CR).