MC68HC08AZ16 Datasheet, PDF (239/527 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Serial Peripheral Interface Module (SPI)
MC68HC08AZ32
238
SPMSTR — SPI master
This read/write bit selects master mode operation or slave mode
operation. Reset sets the SPMSTR bit.
1 = Master mode
0 = Slave mode
CPOL — Clock polarity
This read/write bit determines the logic state of the SPSCK pin
between transmissions. See Figure 4 and Figure 6. To transmit data
between SPI modules, the SPI modules must have identical CPOL
bits. Reset clears the CPOL bit.
CPHA — Clock phase
This read/write bit controls the timing relationship between the serial
clock and SPI data. See Figure 4 and Figure 6. 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 one between bytes. See Figure 12. 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 Mode fault error on page 224. A ‘1’ on the
SS pin does not affect the state of the SPI state machine in any way.
SPWOM — SPI wired-OR mode
This read/write bit disables the pull-up devices on pins SPSCK,
MOSI, and MISO so that those pins become open-drain outputs.
1 = Wired-OR SPSCK, MOSI, and MISO pins
Serial Peripheral Interface Module (SPI)
30-spi
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