Companding Mode; Figure 359. Data Companding Hardware In An Audio Block In The Sai - ST STM32F423 Reference Manual

Serial audio interface (SAI)
30.12.3

Companding mode

Telecommunication applications may require to process the data to transmit or to receive
with a data companding algorithm.
Depending on the COMP[1:0] bit in the SAI_xCR2 register (used only when TDM mode is
selected), the software may choose to process or not the data before sending it on SD serial
output line (compression) or to expand the data after the reception on SD serial input line
(expansion) as illustrated in
Law and the A-Law log which are a part of the CCITT G.711 recommendation.
The companding standard employed in the United States and Japan is the µ-Law and allows
14 bits of dynamic range (COMP[1:0] = 10 in the SAI_xCR2 register).
The European companding standard is A-Law and allows 13 bits of dynamic range
(COMP[1:0] = 11 in the SAI_xCR2 register).
Companding standard (µ-Law or A-Law) can be computed based on 1's complement or 2's
complement representation depending on the CPL bit setting in the SAI_xCR2 register.
The µ-Law and A-Law formats encode data into 8-bit code elements with MSB alignment.
Companded data is always 8 bits wide. For this reason, bit DS[2:0] in the SAI_xCR1 register
will be forced to 010 when the SAI audio block is enabled (bit SAIxEN = 1 in the SAI_xCR1
register) and when the COMP[1:0] bit selects one of these two companding modes.
If no companding processing is required, COMP[1:0] bit in the SAI_xCR2 register should be
kept cleared.
Note: Not applicable when AC'97 selected.
Expansion or compression mode is automatically selected by the SAI configuration.
• If the SAI audio block is configured to be a transmitter, and if the COMP[1] bit is set in
the SAI_xCR2 register, the compression mode will be applied.
•
If the SAI audio block is declared as a receiver, the expansion algorithm will be applied.
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Figure

Figure 359. Data companding hardware in an audio block in the SAI

359,.The two companding modes supported are the µ-
RM0430 Rev 8
RM0430