Output Data Line Management On An Inactive Slot - ST STM32F413 Reference Manual

Serial audio interface (SAI)
30.12.4

Output data line management on an inactive slot

In transmitter mode, it is possible to choose the behavior of the SD line in output when an
inactive slot is sent on the data line (via bit TRIS in the SAI_xCR2 register when the SAI is
disabled).
•
Either the SAI forces 0 on the SD output line when an inactive slot is transmitted, or
•
The line is released in HI-z state at the end of the last bit of data transferred, to release
the line for other transmitters connected to this node.
It is important to note that the two transmitters do not attempt to drive the same SD output
pin simultaneously, which could result in a short circuit. In order to ensure a gap between
transmissions, if the data is lower than 32-bit, the data can be extended to 32-bit by setting
bit SLOTSZ[1:0] = 10 in the SAI_xSLOTR register. Then, the SD output pin will be tristated
at the end of the LSB of the active slot (during the padding to 0 phase to extend the data to
32-bit) if the following slot is declared inactive.
In addition, if the number of slots multiplied by the slot size is lower than the frame length,
the SD output line will be tristated when the padding to 0 is done to complete the audio
frame.
Figure 346
970/1284
illustrates these behaviors.
DocID029473 Rev 3
RM0430