Figure 285. Fs Role Is Start Of Frame + Channel Side Identification (Fsdef = Tris = 1); Figure 286. Fs Role Is Start Of Frame (Fsdef = 0) - ST STM32F405 Reference Manual

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Figure 285. FS role is start of frame + channel side identification (FSDEF = TRIS = 1)

Number of slots not aligned with the audio frame

Number of slots aligned with the audio frame

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.

Data = 0 after slot n if TRIS = 0

SD output released (HI-Z) after slot n if TRIS = 1

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.

Half of frame

Slot 1 OFF Slot 2 ON

Half of frame

RM0090 Rev 18

Slot 3 ON Slot 4 OFF Slot 5 ON

Serial audio interface (SAI)

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