Slot Configuration; Figure 357. Fs Role Is Start Of Frame (Fsdef = 0) - ST STM32F446 Series Reference Manual

RM0390
The FS signal is not used when the audio block in transmitter mode is configured to get the
SPDIF output on the SD line. The corresponding FS I/O will be released and left free for
other purposes.
28.3.7

Slot configuration

The slot is the basic element in the audio frame. The number of slots in the audio frame is
equal to NBSLOT[3:0] + 1.
The maximum number of slots per audio frame is fixed at 16.
For AC'97 protocol or SPDIF (when bit PRTCFG[1:0] = 10 or PRTCFG[1:0] = 01), the
number of slots is automatically set to target the protocol specification, and the value of
NBSLOT[3:0] is ignored.
Each slot can be defined as a valid slot, or not, by setting SLOTEN[15:0] bits of the
SAI_xSLOTR register.
When a invalid slot is transferred, the SD data line is either forced to 0 or released to HI-z
depending on TRIS bit configuration (refer to
slot) in transmitter mode. In receiver mode, the received value from the end of this slot is
ignored. Consequently, there will be no FIFO access and so no request to read or write the
FIFO linked to this inactive slot status.
The slot size is also configurable as shown in
setting SLOTSZ[1:0] bits in the SAI_xSLOTR register. The size is applied identically for
each slot in an audio frame.

Figure 357. FS role is start of frame (FSDEF = 0)

RM0390 Rev 4
Serial audio interface (SAI)
Output data line management on an inactive
Figure 358. The size of the slots is selected by
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