DocID024597 Rev 3 1323/1693
RM0351 Serial audio interface (SAI)
1362
The following table shows how to select the proper synchronization signal depending on the
SAI block used. For example SAI2 can select the synchronization from SAI1 by setting SAI2
SYNCIN to 0. If SAI1 wants to select the synchronization coming from SAI2, SAI1 SYNCIN
must be set to 1. Positions noted as ‘res’ shall not be used.
39.3.4 Audio data size
The audio frame can target different data sizes by configuring bit DS[2:0] in the SAI_xCR1
register. The data sizes may be 8, 10, 16, 20, 24 or 32 bits. During the transfer, either the
MSB or the LSB of the data are sent first, depending on the configuration of bit LSBFIRST in
the SAI_xCR1 register.
39.3.5 Frame synchronization
The FS signal acts as the Frame synchronization signal in the audio frame (start of frame).
The shape of this signal is completely configurable in order to target the different audio
protocols with their own specificities concerning this Frame synchronization behavior. This
reconfigurability is done using register SAI_xFRCR. Figure 437 illustrates this flexibility.
Figure 437. Audio frame
In AC’97 mode or in SPDIF mode (bit PRTCFG[1:0] = 10 or PRTCFG[1:0] = 01 in the
SAI_xCR1 register), the frame synchronization shape is forced to match the AC’97 protocol.
The SAI_xFRCR register value is ignored.
Each audio block is independent and consequently each one requires a specific
configuration.
Table 208. External Synchronization Selection
Block instance SYNCIN= 3 SYNCIN= 2 SYNCIN= 1 SYNCIN= 0
SAI1 res res SAI2 sync res
SAI2 res res res SAI1 sync
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