MC33999 Datasheet, PDF (12/21 Pages) Motorola, Inc – 16-Output Switch with SPI and PWM Control

FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
MCU INTERFACE DESCRIPTION
In operation the 33999 functions as a 16-output serial
switch serving as a microcontroller unit (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.
The 33999 directly interfaces to an MCU, operating at
system clock serial frequencies up to 6.0 MHz using a Serial
Peripheral Interface (SPI) for control and diagnostic readout.
Figure 9 illustrates the basic SPI configuration between an
MCU and one 33999.
33999. Data from the MCU is clocked daisy chain through
each device while the Chip Select bit (CS) is commanded low
by the MCU. During each clock cycle, output status from the
daisy-chained 33999s is being transferred back 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. Daisy chain control of the 33999 requires
24 bits per device.
MC68HCXX
Microcontroller
MC68HCXX
Microcontroller
33999
Shift Register
Receive
Buffer
Parallel
Ports
MOSI
MISO
SI
24-Bit Shift Register
SO
SCLK
RST
CS
PWM
To Logic
Figure 9. 33999 SPI Interface with Microcontroller
All inputs are compatible with 3.3 V/ 5.0 V CMOS logic
levels and incorporate positive logic. An input programmed to
a logic low state (< 0.8 V) has the corresponding output OFF.
Conversely, an input programmed to a logic high state
(> 2.2 V) has the output being controlled ON. Diagnostics is
treated in a similar manner—outputs with a fault will feed
back (via SO) to the microcontroller a logic [1], while normal
operating outputs will provide a logic [0].
The 33999 may be controlled and provide diagnostics
using a daisy chain configuration or in parallel mode.
Figure 10 shows the daisy chain configuration using the
Shift Register
MOSI
MISO
SCLK
Parallel
Ports
PWM1
PWM2
33999
SI
SO
SCLK
CS
PWM
RST
33999
SI
SO
SCLK
CS
PWM
RST
Figure 10. 33999 SPI System Daisy Chain
Multiple 33999 devices can be controlled in a parallel input
fashion using the SPI. Figure 11, page 13, illustrates
potentially 32 loads being controlled by two dedicated
parallel MCU ports used for chip select.
33999
12
Analog Integrated Circuit Device Data
Freescale Semiconductor