Serial Peripheral Interface Module (SPI)
I/O Signals
MC68HC908GP32
•
MC68HC08GP32
—
Rev. 6
Technical Data
MOTOROLA
Serial Peripheral Interface Module (SPI)
327
When an SPI is configured as a master, the SS input can be used in
conjunction with the MODF flag to prevent multiple masters from driving
MOSI and SPSCK.
(See
20.8.2 Mode Fault Error
.) For the state of the
SS pin to set the MODF flag, the MODFEN bit in the SPSCK register
must be set. If the MODFEN bit is low for an SPI master, the SS pin can
be used as a general-purpose I/O under the control of the data direction
register of the shared I/O port. With MODFEN high, it is an input-only pin
to the SPI regardless of the state of the data direction register of the
shared I/O port.
The CPU can always read the state of the SS pin by configuring the
appropriate pin as an input and reading the port data register.
(See
Table 20-3
.)
20.13.5 CGND (Clock Ground)
CGND is the ground return for the serial clock pin, SPSCK, and the
ground for the port output buffers. It is internally connected to V
SS
as
shown in
Table 20-1
.
Table 20-3. SPI Configuration
SPE
SPMSTR
MODFEN
SPI Configuration
State of SS Logic
0
X
(1)
X
Not enabled
General-purpose I/O;
SS ignored by SPI
1
0
X
Slave
Input-only to SPI
1
1
0
Master without MODF
General-purpose I/O;
SS ignored by SPI
1
1
1
Master with MODF
Input-only to SPI
Note 1. X = Don’t care
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Freescale Semiconductor, Inc.
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