MC33972A FREESCALE [Freescale Semiconductor, Inc], MC33972A Datasheet - Page 24

• Manufacturer Part Number: MC33972A
• Description: Multiple Switch Detection Interface with Suppressed Wake-Up
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

from first device is connected to SI of second device). With
two devices, 48 clock pulses are required to shift data in.
When the
both
power supply. The
interrupt pin on the MCU or may have their own dedicated
interrupt to the MCU.
sending the sleep command. With the devices connected in
serial and the sleep command sent, both will enter Sleep
Mode on the rising edge of
the
WAKE
command (
With this event the device that detects this input will not
transition to Sleep Mode, while the second device will enter
Sleep Mode. In this case two switch status commands must
be sent to receive accurate switch status data. The first
switch status command will wake the device in Sleep Mode.
Switch status data may not be valid from the first switch
status command because of the time required for the input
voltage to rise above the 4.0V input comparator threshold.
This time is dependant on the impedance of SGn or SPn
node. The second switch status command will provide
accurate switch status information. It is recommended that
software wait 10ms to 20ms between the two switch status
commands, allowing time for switch input voltages to
stabilize. With all switch states acknowledged by the MCU,
the sleep sequence may be initiated. All parameters for Sleep
Mode should be updated prior to sending the sleep
command.
A POR circuit monitors the internal 5.0V supply. In the event
24
33972
TYPICAL APPLICATIONS
INTRODUCTION
The transition from Normal to Sleep Mode is done by
A condition exists where the MCU is sending the sleep
The 33972 IC has an internal 5.0V supply from V
WAKE
WAKE
pin will transition LOW, waking the other device.
WAKE
pin will be logic [1]. If either device wakes up, the
CS
pins should be connected to the enable pin on the
logic [0]) and a switch input changes state.
feature is used to enable the power supply,
INT
pins may be connected to one
CS
. When Sleep Mode is entered,
PWR
pin.
of transients on the V
Upon reset the 33972 will enter Normal Mode with the
internal registers as defined in
it is recommended that the MCU periodically update all
registers internal to the IC.
USING THE
designed to control an enable pin on system power supply.
While in the Normal Mode, the
enabling the power supply. In the Sleep Mode, the
is high, disabling the power supply. The
passive pull-up to the internal 5.0V supply but may be pulled
up through a resistor to the V
page 25)
pulled up to the V
Figure
pin LOW, causing the 33972 to enter the Normal Mode. The
power supply will then be activated, supplying power to the
VDD pin and the microprocessor and the 33972. The
microprocessor can determine the source of the wake-up by
reading the interrupt flag.
COST AND FLEXIBILITY
interfaces have many discrete components. Discrete
components on standard PWB consume board space and
must be checked for solder joint integrity. An integrated
approach reduces solder joints, consumes less board space,
and offers wider operating voltage, analog interface
capability, and greater interfacing flexibility.
The 33972 provides a
When the WAKE output is not used, the pin should be
During the Sleep Mode, a switch closure will set the
Systems requiring a significant number of switch
16, page 25.
WAKE
DD
supply through a resistor as shown in
PWR
FEATURE
Analog Integrated Circuit Device Data
WAKE
pin, an internal reset may occur.
PWR
Table
WAKE
output and wake-up input
supply (see
Freescale Semiconductor
15, page 18. Therefore
output is LOW,
WAKE
Figure
pin has a
WAKE
17,
WAKE
pin