Figure 337. Functional Block Diagram - ST STM32F413 Reference Manual

Serial audio interface (SAI)
The SAI is mainly composed of two audio sub-blocks with their own clock generator. Each
audio block integrates a 32-bit shift register controlled by their own functional state machine.
Data are stored or read from the dedicated FIFO. FIFO may be accessed by the CPU, or by
DMA in order to leave the CPU free during the communication. Each audio block is
independent. They can be synchronous with each other.
An I/O line controller manages each dedicated pins for a given audio block in the SAI. If the
two blocks are synchronized, this controller reduces the number of I/Os used, freeing up an
FS pin, an SCK pin and eventually an MCLK pin, making them general purpose I/Os.
The functional state machine can be configured to address a wide range of audio protocols.
Some registers are present to set-up the desired protocols (audio frame waveform
generator).
The audio block can be a transmitter or receiver, in master or slave mode. The master mode
means the bit clock SCK and the frame synchronization signal are generated from the SAI,
whereas in slave mode, they come from another external or internal master. There is a
particular case for which the FS signal direction is not directly linked to the master or slave
mode definition. In AC'97 protocol, it will be an SAI output even if the SAI (link controller) is
set-up to consume the SCK clock (and so to be in Slave mode).
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Figure 337. Functional block diagram

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