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M451
May. 4, 2018
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The CLKPOL (SPI_CTL[3]) defines the SPI clock idle state. If CLKPOL = 1, the output of SPI
clock is high at idle state; if CLKPOL = 0, it is low at idle state.
TXNEG (SPI_CTL[2]) defines the data transmitted out either on negative edge or on positive edge
of SPI clock.
RXNEG (SPI_CTL[1]) defines the data received either on negative edge or on positive edge of
SPI clock.
Note:
The settings of TXNEG and RXNEG are mutual exclusive. In other words, do not transmit
and receive data at the same clock edge.
Transmit/Receive Bit Length
The bit length of a transaction word is defined in DWIDTH (SPI_CTL[12:8]) and can be configured
up to 32-bit length in a transaction word for transmitting and receiving.
When SPI controller finishes a transaction, i.e. receives or transmits a special count of bits
defined in DWIDTH (SPI_CTL[12:8]), the unit transfer interrupt flag will be set to 1.
SPIn_CLK
SPIn_MISO
SPIn_MOSI
TX[30]
TX[16]
TX[15] TX[14]
LSB
TX[0]
RX[30]
RX[16]
RX[14]
LSB
RX[0]
MSB
RX[31]
RX[15]
MSB
TX[31]
SPIn_SS
Figure 6.16-632-Bit in One Transaction (Master Mode)
LSB/MSB First
LSB (SPI_CTL[13]) defines the bit transfer sequence in a transaction. If the LSB (SPI_CTL[13]) is
set to 1, the transfer sequence is LSB first. The bit 0 will be transferred firstly. If the LSB
(SPI_CTL[13]) is cleared to 0, the transfer sequence is MSB first.
Suspend Interval
SUSPITV (SPI_CTL[7:4]) provide 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 is 0x3 (3.5 SPI clock
cycles).
Automatic Slave Selection
6.16.5.2
In Master mode, if AUTOSS (SPI_SSCTL[3]) is set, the slave selection signal will be generated
automatically and output to the SPIn_SS pin according to whether SS (SPI_SSCTL[0]) is enabled
or not. The slave selection signal will be set to active state by the SPI controller when the SPI
data transfer is started by writing to FIFO. It will be set to inactive state when SPI bus is idle. If
SPI bus is not idle, i.e. TX FIFO, TX shift register or TX skew buffer is not empty, the slave
selection signal will be set to inactive state between transactions if the value of SUSPITV
(SPI_CTL[7:4]) is greater than or equal to 3.
In Master mode, if the value of SUSPITV is less than 3 and the AUTOSS is set as 1, the slave
Содержание ARM Cortex NuMicro M451 Series
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