Datasheet

Chapter 12 Serial Peripheral Interface (S08SPIV3)
MC9S08AW60 Data Sheet, Rev 2
Freescale Semiconductor 201
12.0.1 Features
Features of the SPI module include:
• Master or slave mode operation
• Full-duplex or single-wire bidirectional option
• Programmable transmit bit rate
• Double-buffered transmit and receive
• Serial clock phase and polarity options
• Slave select output
• Selectable MSB-first or LSB-first shifting
12.0.2 Block Diagrams
This section includes block diagrams showing SPI system connections, the internal organization of the SPI
module, and the SPI clock dividers that control the master mode bit rate.
12.0.2.1 SPI System Block Diagram
Figure 12-2 shows the SPI modules of two MCUs connected in a master-slave arrangement. The master
device initiates all SPI data transfers. During a transfer, the master shifts data out (on the MOSI pin) to the
slave while simultaneously shifting data in (on the MISO pin) from the slave. The transfer effectively
exchanges the data that was in the SPI shift registers of the two SPI systems. The SPSCK signal is a clock
output from the master and an input to the slave. The slave device must be selected by a low level on the
slave select input (
SS pin). In this system, the master device has configured its SS pin as an optional slave
select output.
Figure 12-2. SPI System Connections
7 6 5 4 3 2 1 0
SPI SHIFTER
CLOCK
GENERATOR
7 6 5 4 3 2 1 0
SPI SHIFTER
SS
SPSCK
MISO
MOSI
SS
SPSCK
MISO
MOSI
MASTER
SLAVE