Freescale Semiconductor, Inc.
Multiple Serial Interface
14.5.4 Bidirectional Mode (MOMI or SISO)
In bidirectional mode, the SPI uses only one serial data pin for external
device interface. The MSTR bit decides which pin to be used. The MOSI
pin becomes serial data I/O (MOMI) pin for the master mode, and the
MISO pin becomes serial data I/O (SISO) pin for the slave mode. The
direction of each serial I/O pin depends on the corresponding DDRS bit.
When SPE=1
Master Mode
MSTR=1
Slave Mode
MSTR=0
Serial Out
Serial In
MO
MI
SI
SO
SI
DDRS4
SPI
SPI
DDRS5
Serial In
Serial Out
Normal
Mode
SPC0=0
Serial Out
Serial In
MO
MI
DDS4
SPI
SPI
DDS5
Serial In
Serial Out
SO
SWOM enables open drain output.
SWOM enables open drain output.
Serial Out
Serial In
MOMI
PS4
PS5
SISO
PS5
DDRS4
SPI
SPI
DDRS5
Serial In
Serial Out
Bidirectional
Mode
SPC0=1
Serial Out
Serial In
MOMI
DDS4
SPI
SPI
DDS5
Serial In
Serial Out
PS4
SISO
SWOM enables open drain output. PS4 becomes GPIO.
SWOM enables open drain output. PS5 becomes GPIO.
Figure 14-6. Normal Mode and Bidirectional Mode
Technical Data
MC68HC912DG128 — Rev 3.0
Multiple Serial Interface
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