DocID13902 Rev 15 692/1128
RM0008 Serial peripheral interface (SPI)
742
25.2.2 I
2
S features
• Half-duplex communication (only transmitter or receiver)
• Master or slave operations
• 8-bit programmable linear prescaler to reach accurate audio sample frequencies (from
8 kHz to 192 kHz)
• Data format may be 16-bit, 24-bit or 32-bit
• Packet frame is fixed to 16-bit (16-bit data frame) or 32-bit (16-bit, 24-bit, 32-bit data
frame) by audio channel
• Programmable clock polarity (steady state)
• Underrun flag in slave transmission mode and Overrun flag in reception mode (master
and slave)
• 16-bit register for transmission and reception with one data register for both channel
sides
• Supported I
2
S protocols:
–I
2
S Phillps standard
– MSB-justified standard (left-justified)
– LSB-justified standard (right-justified)
– PCM standard (with short and long frame synchronization on 16-bit channel frame
or 16-bit data frame extended to 32-bit channel frame)
• Data direction is always MSB first
• DMA capability for transmission and reception (16-bit wide)
• Master clock may be output to drive an external audio component. Ratio is fixed at
256 × F
S
(where F
S
is the audio sampling frequency)
• In connectivity line devices, both I
2
S (I2S2 and I2S3) have a dedicated PLL (PLL3) to
generate an even more accurate clock.
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