MC68HC08AS32A Datasheet, PDF (235/296 Pages) Motorola, Inc – Microcontrollers

Freescale Semiconductor, Inc.
Serial Peripheral Interface (SPI)
I/O Registers
CPHA — Clock Phase Bit
This read/write bit controls the timing relationship between the serial clock and
SPI data. (See Figure 15-5 and Figure 15-7.) 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 15-13.) 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 15.6.2 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
SPE — SPI Enable Bit
This read/write bit enables the SPI module. Clearing SPE causes a partial reset
of the SPI. (See 15.9 Resetting the SPI.) Reset clears the SPE bit.
1 = SPI module enabled
0 = SPI module disabled
SPTIE— SPI Transmit Interrupt Enable Bit
This read/write bit enables CPU interrupt requests generated by the SPTE bit.
SPTE is set when a byte transfers from the transmit data register to the shift
register. Reset clears the SPTIE bit.
1 = SPTE CPU interrupt requests enabled
0 = SPTE CPU interrupt requests disabled
MC68HC08AS32A — Rev. 1
MOTOROLA
Serial Peripheral Interface (SPI)
For More Information On This Product,
Go to: www.freescale.com
Data Sheet
235