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MCU-DSP Receive/Transmit Protocol in Slave Mode
SPRU760B
The protocol is made up of several steps:
Step 1: MCU-DSP writes to the setup registers (SPI_SET1 and SPI_SET2).
Step 2: MCU-DSP writes to the transmit register (SPI_TX) (optional).
This is necessary only when you want to perform a transmission at the
same time.
Step 3: MCU-DSP writes to the control register (SPI_CTRL).
Once the RD bit is set, the transmit register (SPI_TX) is copied into
the shift register (SPI_SR).
If CEi = 0 in SPI_SET2, the transmission and reception start as soon
as the slave device enable goes low (nSPEN0) and the shift register
clock is activated (SRCLK).
One cycle later, the RD bit is reset.
The WR bit has no effect on the behavior. This bit is reset like RD,
if it has been set.
Step 4:
When the reception is completed:
The device enable goes high (nSPEN0) if CEi = 0 in SPI_SET2.
-
RE status bit is set in the interrupt status register (SPI_ISR).
-
The shift register (SPI_SR) is copied into the receive register
-
(SPI_RX).
An interrupt is generated if MSK0 is set in the interrupt enable
-
register (SPI_IER).
Step 5: Once the MCU-DSP has read the receive register (SPI_RX) and has
cleared the RE status bit (SPI_ISR), the interrupt request is re-
leased.
SPI Master/Slave
Serial Interfaces
35
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