Figure 360. Tristate Strategy On Sd Output Line On An Inactive Slot - ST STM32F423 Reference Manual

Serial audio interface (SAI)
When the selected audio protocol uses the FS signal as a start of frame and a channel side
identification (bit FSDEF = 1 in the SAI_xFRCR register), the tristate mode is managed
according to
half frame length > number of slots/2, and NBSLOT=6).
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Figure 360. Tristate strategy on SD output line on an inactive slot

Figure 361 (where bit TRIS in the SAI_xCR1 register = 1, and FSDEF=1, and
RM0430 Rev 8
RM0430