33880_12 Datasheet, PDF (15/25 Pages) Freescale Semiconductor, Inc – Configurable Octal Serial Switch with Serial Peripheral Interface I/O

FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
MCU INTERFACE DESCRIPTION
In operation, the 33880 functions as an eight-output serial
switch serving as a microcontroller (MCU) bus expander and
buffer, with fault management and fault reporting features. In
doing so, the device directly relieves the MCU of the fault
management functions. This device directly interfaces to an
MCU using a Serial Peripheral Interface (SPI) for control and
diagnostic readout. Figure 21 and Figure 24, page 16,
illustrate the basic SPI configuration between an MCU and
one 33880.
MC68HCxx
Microcontroller
33880
Shift Register
MOSI
MISO
DI
Shift Register
DO
Receive
Buffer
Parallel
Ports
SCLK
CS
To
Logic
Figure 21. SPI Interface with Microcontroller
All inputs are compatible with 5.0 V and 3.3 V CMOS logic
levels and incorporate positive logic. Whenever an input is
programmed to a logic low state (<0.8 V) the corresponding
output will be OFF. Conversely, whenever an input is
programmed to a logic high state (>2.2 V), the output being
controlled will be ON. Diagnostics are treated in a similar
manner. Outputs with a fault will feedback (via DO) to the
microcontroller as a logic [1] while normal operating outputs
will provide a logic [0].
Figure 22 illustrates the Daisy Chain configuration using
the 33880. Data from the MCU is clocked daisy chain through
each device while the Chip Select (CS) bit is commanded low
by the MCU. During each clock cycle output status from the
daisy chain, the 33880 is being transferred to the MCU via the
Master In Slave Out (MISO) line. On rising edge of CS data
stored in the input register is then transferred to the output
driver.
SCLK
Parallel Port
MC68xx
MCU
with
SPI
Interface
MISO ^CS
DO DI
33880
CS SCLK
DO DI
33880
CS SCLK
DO DI
33880
8 Outputs
8 Outputs
8 Outputs
MOSI
Figure 22. 33880 SPI System Daisy Chain
Multiple 33880 devices can be controlled in a parallel input
fashion using the SPI. Figure 23 illustrates 24 loads being
controlled by three dedicated parallel MCU ports used for
chip select.
MOSI
SCLK
MISO
MC68xx
Microcontroller
SPI
DI
SCLK
DO
CS
8 Outputs
DI
SCLK
DO
CS
8 Outputs
A
Parallel
Ports
B
C
DI
SCLK
DO
CS
8 Outputs
Figure 23. Parallel Input SPI Control
Analog Integrated Circuit Device Data
Freescale Semiconductor
33880
15