Motorola MPC8260 User Manual
MOTOROLA
Chapter 33. Serial Peripheral Interface (SPI)
33-3
Part IV. Communications Processor Module
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When the SPI is a slave, SPICLK is the clock input that shifts received data in from
SPIMOSI and transmitted data out through SPIMISO. SPISEL is the enable input to
the SPI slave. In a multimaster environment, SPISEL (always an input) is used to
detect an error when more than one master is operating.
SPIMOSI and transmitted data out through SPIMISO. SPISEL is the enable input to
the SPI slave. In a multimaster environment, SPISEL (always an input) is used to
detect an error when more than one master is operating.
As described in Chapter 35, ÒParallel I/O Ports,Ó SPIMISO, SPIMOSI, SPICLK, and
SPISEL are multiplexed with port B[28Ð31] signals, respectively. They are conÞgured as
SPI signals through the port B signal assignment register (PBPAR) and the Port B data
direction register (PBDIR), speciÞcally by setting PBPAR[DDn] and PBDIR[DRn].
SPISEL are multiplexed with port B[28Ð31] signals, respectively. They are conÞgured as
SPI signals through the port B signal assignment register (PBPAR) and the Port B data
direction register (PBDIR), speciÞcally by setting PBPAR[DDn] and PBDIR[DRn].
33.3 ConÞguring the SPI Controller
The SPI can be programmed to work in a single- or multiple-master environment. This
section describes SPI master and slave operation in a single-master conÞguration and then
discusses the multi-master environment.
section describes SPI master and slave operation in a single-master conÞguration and then
discusses the multi-master environment.
33.3.1 The SPI as a Master Device
In master mode, the SPI sends a message to the slave peripheral, which sends back a
simultaneous reply. A single master MPC8260 with multiple slaves can use general-
purpose parallel I/O signals to selectively enable slaves, as shown in Figure 33-2. To
eliminate the multimaster error in a single-master environment, the masterÕs SPISEL input
can be forced inactive by selecting port B[31] for general-purpose I/O
(PBPAR[DD31] = 0).
simultaneous reply. A single master MPC8260 with multiple slaves can use general-
purpose parallel I/O signals to selectively enable slaves, as shown in Figure 33-2. To
eliminate the multimaster error in a single-master environment, the masterÕs SPISEL input
can be forced inactive by selecting port B[31] for general-purpose I/O
(PBPAR[DD31] = 0).
Figure 33-2. Single-Master/Multi-Slave Configuration
SPIMOSI
SPIMISO
SPICLK
SPISEL
Slave 0
SPIMISO
SPICLK
SPISEL
Slave 1
Slave 2
Master SPI
SPIMOSI
SPIMISO
SPICLK
SPISEL
SPIMOSI
The SPISEL
SPICLK
SPIMISO
SPIMOSI
MPC8260
decoder can be
either internal or
external logic.