MC68HC05C9A Datasheet, PDF (65/124 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 10
Serial Peripheral Interface (SPI)
10.1 Introduction
The serial peripheral interface (SPI) is an interface built into the device which allows several M68HC05
microcontroller units (MCU), or M68HC05 MCU plus peripheral devices, to be interconnected within a
single printed circuit board. In an SPI, separate wires are required for data and clock. In the SPI format,
the clock is not included in the data stream and must be furnished as a separate signal. An SPI system
may be configured in one containing one master MCU and several slave MCUs or in a system in which
an MCU is capable of being a master or a slave.
10.2 Features
SPI features include:
• Full-duplex, 4-wire synchronous transfers
• Master or slave operation
• Bus frequency divided by 2 (maximum) master bit frequency
• Bus frequency (maximum) slave bit frequency
• Four programmable master bit rates
• Programmable clock polarity and phase
• End-of-transmission interrupt flag
• Write collision flag protection
• Master-master mode fault protection capability
10.3 SPI Signal Description
The four basic signals (MOSI, MISO, SCK, and SS) are described here. Each signal function is described
for both the master and slave modes.
NOTE
Any SPI output line has to have its corresponding data direction register bit
set. If this bit is clear, the line is disconnected from the SPI logic and
becomes a general-purpose input line. When the SPI is enabled, any SPI
input line is forced to act as an input regardless of what is in the
corresponding data direction register bit.
10.3.1 Master In/Slave Out (MISO)
The MISO line is configured as an input in a master device and as an output in a slave device. It is one
of the two lines that transfer serial data in one direction, with the most significant bit sent first. The MISO
line of a slave device is placed in the high-impedance state if the slave is not selected.
MC68HC05C9A Advance Information Data Sheet, Rev. 5.1
Freescale Semiconductor
65