Serial audio interface (SAI) RM0090
926/1731 DocID018909 Rev 11
Figure 285. FS role is start of frame + channel side identification (FSDEF = TRIS = 1)
1. The frame length should be even.
If bit FSDEF in SAI_xFRCR is kept clear, so FS signal is equivalent to a start of frame, and
if the number of slots defined in bit NBSLOT[3:0] in SAI_xSLOTR multiplied by
the number of bits by slot configured in bit SLOTSZ[1:0] in SAI_xSLOTR is less than the
frame size (bit FRL[7:0] in the SAI_xFRCR register), then,
• if TRIS = 0 in the SAI_xCR2 register, the remaining bit after the last slot will be forced to
0 until the end of frame in case of transmission,
• if TRIS = 1, the line will be released to HI-Z during the transfer of these remaining bits.
In reception mode, these bits are discarded.
Figure 286. FS role is start of frame (FSDEF = 0)
29.8 Slot configuration
The slot is the basic element in the audio frame. The number of slots in the audio frame is
equal to the configured setting of bit NBSLOT[3:0] in the SAI_xSLOTR register +1.
The maximum number of slots per audio frame is fixed at 16.
For AC’97 protocol (when bit PRTCFG[1:0] = 10), the number of slots is automatically set to
target the protocol specification, and the value of NBSLOT[3:0] is ignored.
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