mc33291l Freescale Semiconductor, Inc, mc33291l Datasheet - Page 12

• Manufacturer Part Number: mc33291l
• Description: Eight-output Switch With Serial Peripheral Interface I/o
• Manufacturer: Freescale Semiconductor, Inc

parallel input fashion using SPI, illustrated in
figure shows a possible 24 loads being controlled by only
three dedicated parallel MCU ports used for chip select.
controlling multiple 33291L devices using two MCUs. A
system can have only one master MCU at any given instant
of time and one or more slave MCUs. Master control of the
system must pass from one MCU to the other in an orderly
manner. The master MCU supplies the system clock signal
(top MCU designated the master); the lower MCU being the
slave. It is possible to have a system with more than one
12
33291L
FUNCTIONAL DESCRIPTION
INTRODUCTION
Microcontroller
Multiple 33291L devices can also be controlled in a
Figure
Parallel
Ports
MC68XX
SPI
15, page 13, illustrates a basic method of
Microcontroller
A0
A1
A2
Figure 14. Parallel Input SPI Control
MC68XX
SPI
MOSI
SCLK
SCLK
Parallel Port
MISO
IRQ
MOSI
CS
SO
8 Outputs
SI
SCLK
CS
SI
SCLK
CS
SI
SCLK
CS
33291
Figure 13. 33291L SPI System Daisy Chain
33291
33291
33291
Figure
SCLK
SI
14. This
8 Outputs
8 Outputs
8 Outputs
CS
SO
8 Outputs
33291
master; however, not at the same time. Only when the master
is not communicating can a slave assume the mastership and
communicate. MCU master control is switched through the
use of the slave select (
become a slave when it detects a logic low state on its
applications where a large number of loads require efficient
control. To this end, the popular Synchronous Serial
Peripheral Interface (SPI) protocol is incorporated to
communicate efficiently with the MCU.
SPI SYSTEM ATTRIBUTES
with numerous standard peripherals and MCUs available
from Motorola and other semiconductor manufacturers. SPI
reduces the number of pins necessary for input/output (I/O)
on the 33291L. It also offers an easy means of expanding the
I/O function using few MCU pins. The SPI system of
communication consists of the MCU transmitting, in return it
receives one data-bit of information per system clock cycle.
one pin, Master Out Serial In (MOSI), and received by
another pin, Master In Serial Out (MISO), of the MCU.
• Full duplex, three-wire synchronous data transfer
• Each microcontroller can be a master or a slave
• Provides write collision flag protection
• Provides end of message interrupt flag
• Four I/Os associated with SPI (MOSI, MISO, SCLK, SS)
• An MCU is required for efficient operational control
• In contrast to parallel input control it is slower at performing
SCLK
These basic examples make the 33291L very attractive for
The SPI system is flexible enough to communicate directly
Data bits of information are simultaneously transmitted by
Some features of SPI are as follows:
Drawbacks to SPI are as follows:
pulse width modulating (PWM) functions.
SI
CS
SO
8 Outputs
33291
SCLK
Analog Integrated Circuit Device Data
SS
SI
) pin of the MCUs. A master will
Freescale Semiconductor
CS
SO
8 Outputs
33291
SCLK
SI
SS
pin.