MC68HC08AS32 Datasheet, PDF (303/394 Pages) Motorola, Inc – M68HC08 Family of 8-bit microcontroller units (MCUs)

Serial Peripheral Interface (SPI)
I/O Registers
CPOL — Clock Polarity Bit
This read/write bit determines the logic state of the SPSCK pin
between transmissions. (See Figure 18-3 and Figure 18-5.) To
transmit data between SPI modules, the SPI modules must have
identical CPOL bits. Reset clears the CPOL bit.
CPHA — Clock Phase Bit
This read/write bit controls the timing relationship between the serial
clock and SPI data. (See Figure 18-3 and Figure 18-5.) To transmit
data between SPI modules, the SPI modules must have identical
CPHA bits. When CPHA = 0, the SS pin of the slave SPI module must
be set to logic 1 between bytes. (See Figure 18-11.) Reset sets the
CPHA bit.
When CPHA = 0 for a slave, the falling edge of SS indicates the
beginning of the transmission. This causes the SPI to leave its idle
state and begin driving the MISO pin with the MSB of its data. Once
the transmission begins, no new data is allowed into the shift register
from the data register. Therefore, the slave data register must be
loaded with the desired transmit data before the falling edge of SS.
Any data written after the falling edge is stored in the data register and
transferred to the shift register at the current transmission.
When CPHA = 1 for a slave, the first edge of the SPSCK indicates the
beginning of the transmission. The same applies when SS is high for
a slave. The MISO pin is held in a high-impedance state, and the
incoming SPSCK is ignored. In certain cases, it may also cause the
MODF flag to be set. (See 18.7.2 Mode Fault Error.) A logic 1 on the
SS pin does not in any way affect the state of the SPI state machine.
SPWOM — SPI Wired-OR Mode Bit
This read/write bit disables the pullup devices on pins SPSCK, MOSI,
and MISO so that those pins become open-drain outputs.
1 = Wired-OR SPSCK, MOSI, and MISO pins
0 = Normal push-pull SPSCK, MOSI, and MISO pins
MC68HC08AS32 — Rev. 3.0
MOTOROLA
Serial Peripheral Interface (SPI)
Advance Information
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