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NUC126
Aug. 08, 2018
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Rev 1.03
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In SPI Master mode, if the value of SUSPITV (USPI_PROTCTL[11:8]) is less than 3 and the AUTOSS
(USPI_PROTCTL[3]) is set as 1, the slave select signal will be kept at active state between two
successive word transactions.
In SPI Slave mode, to recognize the inactive state of the slave select signal, the inactive period of the
received slave select signal must be larger than 2 peripheral clock cycles between two successive
transactions.
SPI_SS
(USCIx_CTL0)
TXEMPTY
(USPI_BUFSTS[8])
CTLOINV
(USPI_LINECTL[7])
SPI_CLK
(USCIx_CLK)
SS
(USPI_PROTCTL[2])
Note: Automatic slave select is enabled
1 SPI clock
1.5 SPI clock
Figure 6.21-12 Auto Slave Select (SUSPITV
≧
0x3)
SPI_SS
(USCIx_CTL0)
TXEMPTY
(USPI_BUFSTS[8])
CTLOINV
(USPI_LINECTL[7])
SPI_CLK
(USCIx_CLK)
SS
(USPI_PROTCTL[2])
Note: Automatic slave select is enabled
One word
transaction
One word
transaction
Figure 6.21-13 Auto Slave Select (SUSPITV < 0x3)
6.21.5.8 Slave 3-wire Mode
When the SLV3WIRE (USPI_PROTCTL[1]) is set by software to enable the Slave 3-wire mode, the
USCI SPI communication can work with no slave select signal in Slave mode. The SLV3WIRE
(USPI_PROTCTL[1]) only takes effect in SPI Slave mode. Only three pins, SPI_CLK (through
USCIx_CLK line), SPI_MOSI (through USCIx_DAT0 line), and SPI_MISO (through USCIx_DAT1 line),