Datasheet

Serial Peripheral Interface (SPI)
Functional Description
MC68HC908GR8 — Rev 4.0 Technical Data
MOTOROLA Serial Peripheral Interface (SPI) 301
The following paragraphs describe the operation of the SPI module.
20.5.1 Master Mode
The SPI operates in master mode when the SPI master bit, SPMSTR, is
set.
NOTE: Configure the SPI modules as master or slave before enabling them.
Enable the master SPI before enabling the slave SPI. Disable the slave
SPI before disabling the master SPI. See SPI Control Register.
Only a master SPI module can initiate transmissions. Software begins
the transmission from a master SPI module by writing to the transmit
data register. If the shift register is empty, the byte immediately transfers
to the shift register, setting the SPI transmitter empty bit, SPTE. The byte
begins shifting out on the MOSI pin under the control of the serial clock.
See Figure 20-3.
Figure 20-3. Full-Duplex Master-Slave Connections
SHIFT REGISTER
SHIFT REGISTER
BAUD RATE
GENERATOR
MASTER MCU SLAVE MCU
V
DD
MOSI MOSI
MISO MISO
SPSCK SPSCK
SS
SS
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