MC68HC912BL16 Datasheet, PDF (97/128 Pages) Freescale Semiconductor, Inc – 16-Bit Microcontroller

Freescale Semiconductor, Inc.
13.3.3 SS Output
Available in master mode only, SS output is enabled with the SSOE bit in the SP0CR1 register if the
corresponding DDRS bit is set. The SS output pin will be connected to the SS input pin of the external
slave device. The SS output automatically goes low for each transmission to select the external device
and it goes high during each idling state to deselect external devices.
DDS7
0
0
1
1
Table 31 SS Output Selection
SSOE
0
1
0
1
Master Mode
SS Input with MODF Feature
Reserved
General-Purpose Output
SS Output
Slave Mode
SS Input
SS Input
SS Input
SS Input
13.3.4 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
Normal
Mode
SPC0=0
Serial Out
MO
SPI
DDS5
Serial In
MI
SWOM enables open drain output.
Serial In
SI
SPI
DDS4
Serial Out
SO
SWOM enables open drain output.
Bidirectional
Mode
SPC0=1
Serial Out
SPI
Serial In
DDS5
MOMI
PS4
SWOM enables open drain output. PS4 becomes GPIO.
Serial In
SPI
Serial Out
DDS4
PS5
SISO
SWOM enables open drain output. PS5 becomes GPIO.
Figure 26 Normal Mode and Bidirectional Mode
13.3.5 Register Descriptions
Control and data registers for the SPI subsystem are described below. The memory address indicated
for each register is the default address that is in use after reset. The entire 512-byte register block can
be mapped to any 2-Kbyte boundary within the standard 64-Kbyte address space. For more information
refer to 5 Operating Modes and Resource Mapping.
SP0CR1 — SPI Control Register 1
Bit 7
6
5
SPIE
SPE
SWOM
RESET:
0
0
0
4
MSTR
0
3
CPOL
0
2
CPHA
1
1
SSOE
0
Bit 0
LSBF
0
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MC68HC912BL16TS/D
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