RM0091 Serial peripheral interface / inter-IC sound (SPI/I2S)
Doc ID 018940 Rev 1 655/742
Figure 265. I
2
S Philips protocol waveforms (16/32-bit full accuracy, CPOL = 0)
Data are latched on the falling edge of CK (for the transmitter) and are read on the rising
edge (for the receiver). The WS signal is also latched on the falling edge of CK.
Figure 266. I
2
S Philips standard waveforms (24-bit frame with CPOL = 0)
This mode needs two write or read operations to/from the SPIx_DR register.
● In transmission mode:
If 0x8EAA33 has to be sent (24-bit):
Figure 267. Transmitting 0x8EAA33
● In reception mode:
If data 0x8EAA33 is received:
MS19591V1
CK
WS
SD
Transmission Reception
May be 16-bit or 32-bit
MSB
MSBLSB
Channel left
Channel right
MS19592V1
CK
WS
SD
Transmission Reception
24-bit data
MSB
LSB
Channel left 32-bit
Channel right
8-bit remaining 0 forced
MS19593V1
0x8EAA 0x33XX
First write to Data register Second write to Data register
Only the 8 MSB are sent
to compare the 24 bits
8 LSBs have no meaning
and can be anything
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