MC33298 Motorola, MC33298 Datasheet - Page 10

• Manufacturer Part Number: MC33298
• Description: OCTAL SERIAL SWITCH (SPI Input/Output)
• Manufacturer: Motorola

which when coupled to an MCU, receives “on”/“off”
commands from the MCU and in return transmits the drain
status of the device’s output switches. Many devices can be
“daisy–chained” together to form a larger system (see
Figure 12). Note in this example that only one dedicated
MCU parallel port (aside from the required SPI) is needed for
chip select to control 32 possible loads.
parallel input fashion using SPI (see Figure 13). This figure
shows a possible 24 loads being controlled by only three
dedicated parallel MCU ports used for chip select.
MC33298 devices using two MCUs. A system can have only
one master MCU at any given instant of time and one or more
slave MCUs. 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 master but not at the same time. Only when the
master is not communicating can a slave communicate. MCU
master control is switched through the use of the slave select
(SS) pin of the MCUs. A master will become a slave when it
detects a logic low state on its SS pin.
for applications where a large number of loads need be
controlled efficiently. The popular Synchronous Serial
Peripheral Interface (SPI) protocol is incorporated, to this
end, to communicate efficiently with the MCU.
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One main advantage of the MC33298 is the serial port
Multiple MC33298 devices can also be controlled in a
Figure 14 shows a basic method of controlling multiple
These basic examples make the MC33298 very attractive
Microconttoller
MC68XX
Parallel
SPI
Ports
Figure 13. Parallel Input SPI Control
A0
A1
A2
MOSI
SCLK
SI
SCLK
CSB
SI
SCLK
CSB
SI
SCLK
CSB
MC33298
MC33298
MC33298
8 Outputs
8 Outputs
8 Outputs
MC33298
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 MC33298. 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, and in
return, receiving one databit of information per clock cycle.
one pin, Microcontroller Out Serial In (MOSI), and received
by another pin, Microcontroller In Serial Out (MISO), of
the MCU.
efficient operational control and, in contrast to parallel input
control, is slower at performing pulse width modulating
(PWM) functions.
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)
The SPI system is flexible enough to communicate directly
Databits of information are simultaneously transmitted by
Some features of SPI are:
The only drawbacks to SPI are that an MCU is required for
V DD
V DD
B0
B1
B0
B1
SS
SS
Microcontroller
Microcontroller
Figure 14. Multiple MCU SPI Control
8–Bit
8–Bit
(Alternate
MC68XX
MC68XX
(Master)
Parallel
Master)
Parallel
Ports
Ports
SPI
SPI
SCLK
MISO
MOSI
SCLK
MISO
MOSI
MOTOROLA ANALOG IC DEVICE DATA
A0
A1
A2
A0
A1
A2
CSB
SCLK
SO
SI
CSB
SCLK
SO
SI
CSB
SCLK
SO
SI
MC33298
MC33298
MC33298
8–Bit
8–Bit
8–Bit
8 Outputs
8 Outputs
8 Outputs