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DMA Receive Protocol in Slave Mode
SPRU760B
The protocol has several steps:
Step 1: MCU-DSP writes to the setup and control registers (SPI_SET1,
SPI_SET2, and SPI_CTRL).
If CEi = 0 in SPI_SET2 and the RD bit is set, the reception starts
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as soon as the slave device enable goes low (nSPEN0) and the
shift register clock is activated (SRCLK).
Step 2: When the reception is completed:
The device enable goes high (nSPEN0), if CEi = 0 in SPI_SET2.
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The RX_FULL bit is set in the data status register (SPI_DSR).
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The shift register (SPI_SR) is copied into the receive register
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(SPI_RX).
A receive DMA request is generated.
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Step 3: Once the DMA reads the receive register (SPI_RX):
The RX_FULL status bit is reset in the data status register
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(SPI_DSR).
The receive DMA request is released.
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Another reception can start.
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To stop the process, the MCU-DSP must reset the RD bit in the con-
trol register (SPI_CTRL).
SPI Master/Slave
Serial Interfaces
45
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