Serial audio interface (SAI) RM0090
934/1749 RM0090 Rev 18
Each slot can be defined as a valid slot, or not, by setting bit SLOTEN[15:0] in the
SAI_xSLOTR register. In an audio frame, during the transfer of a non-valid slot, 0 value will
be forced on the data line or the SD data line will be released to HI-z (refer to
Section 29.12.4) if the audio block is transmitter, or the received value from the end of this
slot will be 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 the Figure 287. The size of the slots is
selected by setting bit SLOTSZ[1:0] in the SAI_xSLOTR register. The size is applied
identically for each slot in an audio frame.
Figure 287. Slot size configuration with FBOFF = 0 in SAI_xSLOTR
It is possible to choose the position of the first data bit to transfer within the slots, this offset
is configured by bit FBOFF[5:0] in the SAI_xSLOTR register. 0 values will be injected in
transmitter mode from the beginning of the slot until this offset position is reached. In
reception, the bit in the offset phase is ignored. This feature targets the LSB justified
protocol (if the offset is equal to the slot size minus the data size).
Figure 288. First bit offset
MS30033V1
00..00
00..00
X..X
XX.. XX
X: don’t care
Audio block is transmitter
Slot size = data size
data size
data size
data size
data size
slotx
slotx
slotx
16-bit
32-bit
Audio block is receiver
Slot size = data size
data size
data size
data size
slotx
slotx
slotx
16-bit
32-bit
data size
MS30034V1
XX .. XX
00
00..00
X: don’t care
Audio block is transmitter
Slot size = data size
data size
data size
data size
data size
slotx
slotx
slotx
16-bit
32-bit
Audio block is receiver
00
FBOFF
FBOFF = SLOT SZ -DS
XX
Slot size = data size
data size
data size
data size
data size
slotx
slotx
slotx
16-bit
32-bit
XX
FBOFF
FBOFF = SLOT SZ -DS
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