Programming Model
MOTOROLA
Serial Peripheral Interface Modules (SPI 1 and SPI 2)
18-9
SPIEN
Bit 9
SPI Module Enable
—Enables/Disables the serial
peripheral interface. SPIEN must be asserted before an
exchange is initiated. Writing 0 to SPIEN flushes the
receive and transmit FIFOs.
0 = Disable the SPI
1 = Enable the SPI
XCH
Bit 8
Exchange
—Initiates a data exchange in master mode.
XCH remains set while the exchange is in progress, or
while the SPI module is waiting for an active SPI_RDY
control signal input. XCH is automatically cleared when
all data in the TXFIFO and shift register are shifted out.
In slave mode, XCH must be cleared.
0 = Idle
1 = Initiates exchange (write) or busy
(read)
SSPOL
Bit 7
SS Polarity Select
—Selects the polarity of the SS
signal (in both master and slave mode).
0 = Active low
1 = Active high
SSCTL
Bit 6
SS Wave Form Select
—Selects the output wave form
for the SS signal when in master mode.
Controls RXFIFO advancement when in slave mode for
SPI 1 only.
In master mode:
0 = SS stays low between SPI bursts
1 = Insert pulse between SPI bursts
In slave mode:
0 = RXFIFO advanced by BIT_COUNT
1 = RXFIFO advanced by SS rising edge
PHA
Bit 5
Phase
—Controls the clock/data phase relationship
(see Figure 18-2 on page 18-3).
0 = Phase 0 operation
1 = Phase 1 operation
POL
Bit 4
Polarity
—Controls the polarity of the SCLK signal (see
Figure 18-2 on page 18-3).
0 = Active high polarity (0 = idle)
1 = Active low polarity (1 = idle)
BIT_COUNT
Bits 3–0
Bit Count
—Selects the length of the transfer. A
maximum of 16 bits can be transferred.
In master mode, a 16-bit data word is loaded from
TXFIFO to the shift register, however only the least n
bits (n=BIT_COUNT) are shifted out. The next 16-bit
word is then loaded to the shift register.
Controls the number of bits in a receive data word (in
slave mode and when the SSCTL bit is 0). When the
SSCTL bit is 1, this field is “don’t care.”
0000 = 1–bit transfer
0001 = 2–bit transfer
...
1111 = 16–bit transfer
Table 18-6. SPI 1 Control Register and SPI 2 Control Register Description (Continued)
Name
Description
Settings
Содержание DragonBall MC9328MX1
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