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M0A21/M0A23 Series
May 06, 2022
Page
536
of 746
Rev 1.02
M0
A21
/M
0
A
2
3
SE
RIES
TEC
H
NICAL
RE
FEREN
C
E
M
ANUAL
SPI_CLK
(USCIx_CLK)
SPI_MISO
(USCIx_DAT1)
SPI_MOSI
(USCIx_DAT0)
TX[14]
TX[8]
TX[7]
TX[6]
LSB
TX[0]
RX[14]
RX[8]
RX[6]
LSB
RX[0]
MSB
RX[15]
RX[7]
MSB
TX[15]
SPI_SS
(USCIx_CTL0)
Note:
x = 0,1,2
Figure 6.14-1016-bit Data Length in One Word Transaction with MSB First Format
Word Suspend
SUSPITV (USPI_PROTCTL[11:8]) provides a configurable suspend interval, 0.5 ~ 15.5 SPI clock
periods, between two successive transaction words in Master mode. The definition of the suspend
interval is the interval between the last clock edge of the preceding transaction word and the first clock
edge of the following transaction word. The default value of SUSPITV (USPI_PROTCTL[11:8]) is 0x3
(3.5 SPI clock cycles).
SPI_CLK
(USCIx_CLK)
SPI_MISO
(USCIx_DAT1)
SPI_MOSI
(USCIx_DAT0)
TX[14]
LSB
TX[0]
MSB
TX[15]
TX[14]
LSB
TX[0]
RX[14]
LSB
RX[0]
RX[14]
LSB
RX[0]
MSB
RX[15]
Suspend
Interval
1st Transaction Word
2nd Transaction Word
MSB
RX[15]
MSB
TX[15]
Transfer Frame
Suspend
Interval
Note:
Timing Condition is SCLKMODE[1:0] = 0x0; LSB = 0; DWIDTH[3:0] = 0x0;
Note:
x = 0,1
Figure 6.14-11 Word Suspend Interval between Two Transaction Words
Automatic Slave Select Function
AUTOSS (USPI_PROTCTL[3]) is used for SPI Master mode to enable the automatic slave select
function. If the bit AUTOSS (USPI_PROTCTL[3]) is set, the slave select signal will be generated
automatically and the setting value of SS (USPI_PROTCTL[2]) will not affect the output slave select
(through USCIx_CTL0 line). This means that the slave select signal will be asserted by the USCI
controller when the SPI data transfer is started by writing to the transmit buffer. And, it will be de-asserted
after either all transaction is finished or one word transaction done if the value of SUSPITV
(USPI_PROTCTL[11:8]) is equal to or great than 3.
If the AUTOSS bit (USPI_PROTCTL[3]) is cleared, the slave select on USCIx_CTL0 pin will be
asserted/de-asserted by setting/clearing the SS (USPI_PROTCTL[2]). The internal slave select signal
is active high and the CTLOINV (USPI_LINECTL[7]) can be used for the inversion of the slave select
signal.
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