MC68HC908LJ24 Datasheet, PDF (291/464 Pages) Motorola, Inc – Microcontrollers

Freescale Semiconductor, Inc.
Serial Peripheral Interface Module (SPI)
Functional Description
14.5.1 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 14.14.1 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 14-3.)
MASTER MCU
SHIFT REGISTER
BAUD RATE
GENERATOR
MISO
MOSI
SPSCK
SS
MISO
MOSI
SPSCK
V_DD
SS
SLAVE MCU
SHIFT REGISTER
Figure 14-3. Full-Duplex Master-Slave Connections
MC68HC908LJ24/LK24 — Rev. 2
MOTOROLA
Serial Peripheral Interface Module (SPI)
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Data Sheet
291