Datasheet

DocID024030 Rev 10 39/239
STM32F427xx STM32F429xx Functional overview
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3.26 Inter-integrated sound (I
2
S)
Two standard I
2
S interfaces (multiplexed with SPI2 and SPI3) are available. They can be
operated in master or slave mode, in full duplex and simplex communication modes, and
can be configured to operate with a 16-/32-bit resolution as an input or output channel.
Audio sampling frequencies from 8 kHz up to 192 kHz are supported. When either or both of
the I
2
S interfaces is/are configured in master mode, the master clock can be output to the
external DAC/CODEC at 256 times the sampling frequency.
All I2Sx can be served by the DMA controller.
Note: For I2S2 full-duplex mode, I2S2_CK and I2S2_WS signals can be used only on GPIO Port
B and GPIO Port D.
3.27 Serial Audio interface (SAI1)
The serial audio interface (SAI1) is based on two independent audio sub-blocks which can
operate as transmitter or receiver with their FIFO. Many audio protocols are supported by
each block: I2S standards, LSB or MSB-justified, PCM/DSP, TDM, AC’97 and SPDIF
output, supporting audio sampling frequencies from 8 kHz up to 192 kHz. Both sub-blocks
can be configured in master or in slave mode.
In master mode, the master clock can be output to the external DAC/CODEC at 256 times of
the sampling frequency.
The two sub-blocks can be configured in synchronous mode when full-duplex mode is
required.
SAI1 can be served by the DMA controller.
3.28 Audio PLL (PLLI2S)
The devices feature an additional dedicated PLL for audio I
2
S and SAI applications. It allows
to achieve error-free I
2
S sampling clock accuracy without compromising on the CPU
performance, while using USB peripherals.
The PLLI2S configuration can be modified to manage an I
2
S/SAI sample rate change
without disabling the main PLL (PLL) used for CPU, USB and Ethernet interfaces.
The audio PLL can be programmed with very low error to obtain sampling rates ranging
from 8 KHz to 192 KHz.
In addition to the audio PLL, a master clock input pin can be used to synchronize the
I
2
S/SAI flow with an external PLL (or Codec output).
3.29 Audio and LCD PLL(PLLSAI)
An additional PLL dedicated to audio and LCD-TFT is used for SAI1 peripheral in case the
PLLI2S is programmed to achieve another audio sampling frequency (49.152 MHz or
11.2896 MHz) and the audio application requires both sampling frequencies simultaneously.
The PLLSAI is also used to generate the LCD-TFT clock.
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