Motorola MC68HC908MR32 사용자 설명서
Serial Peripheral Interface Module (SPI)
I/O Registers
MC68HC908MR16/MC68HC908MR32 — Rev. 4.0
Advance Information
MOTOROLA
Serial Peripheral Interface Module (SPI)
269
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
appropriate pin as an input and reading the port data register.
See
13.12.5 V
SS
(Clock Ground)
V
SS
is the ground return for the serial clock pin, SPSCK, and the ground
for the port output buffers. To reduce the ground return path loop and
minimize radio frequency (RF) emissions, connect the ground pin of the
slave to the V
minimize radio frequency (RF) emissions, connect the ground pin of the
slave to the V
SS
pin of the master.
13.13 I/O Registers
Three registers control and monitor SPI operation:
•
SPI control register, SPCR
•
SPI status and control register, SPSCR
•
SPI data register, SPDR
Table 13-3. SPI Configuration
SPE
SPMSTR
MODFEN
SPI Configuration
State of SS Logic
0
X
(1)
1. X = don’t care
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