FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
Watchdog Time-out
VDD
RST
Watchdog
Period
WDOG
SPI
WDOG Clear
TIM1 register addressed.
SPI CS
Figure 12. RST and WDOG Output Operation
In order to select and activate the cyclic sense wake-up
from the L0:L3 inputs, the WUR register must be configured
with the appropriate level sensitivity and the LPC register
must be configured with 1xx1 data (bit LX2HS set at 1 and bit
HSAUTO set at 1). The wake-up mode selection (direct or
cyclic sense) is valid for all four wake-up inputs.
WAKE-UP CAPABILITIES
Several wake-up capabilities are available to the SBC
when it is in Sleep or Stop mode. When a wake-up has
occurred, the wake-up event is stored in the Wake-Up
Register (WUR) or the CAN register and read by the MCU to
determine the wake-up source. The wake-up options are
selectable through SPI while the 33742 is in Normal or
Standby mode and prior to entering low power modes (Sleep
or Stop mode). When a wake-up occurs in Sleep mode, the
SBC reactivates VDD supply. It generates an interrupt if
wake-up occurs from Stop mode.
FORCED WAKE-UP
The SBC can wake up automatically after a predetermined
time spent in Sleep or Stop mode. Cyclic Sense and Forced
Wake-up are exclusive. If Forced Wake-Up is enabled (FWU
bit set to 1 in the LPC register), Cyclic Sense cannot be
enabled.
WAKE-UP FROM WAKE-UP INPUTS (L0:L3)
WITHOUT CYCLIC SENSE
CAN INTERFACE WAKE-UP
The wake-up lines are used to determine the state of
external switches and if changes occurred to wake up the
MCU (in Sleep or Stop modes). Wake-up pins L0:L3 are able
to handle up to 40 VDC. The internalize” threshold is 3.0 V
typical and these inputs can be used as an input port
expander. The wake-up input states are read through SPI
(WUR register).
The SBC incorporates a high-speed 1.0 Mbps CAN
physical interface. It is compatible with ISO 11898-2
standard. The operation of the CAN physical interface is
controlled through the SPI. The CAN operating modes are
independent of the 33742 operational modes.
The SBC can wake up from a CAN message if the CAN
wake-up feature is enabled. Refer to the section titled LOGIC
COMMANDS AND REGISTERS beginning on page 42 for
details of the wake-up detection.
In order to select and activate direct wake-up from the
L0:L3 inputs, the WUR register must be configured with the
appropriate level sensitivity. Additionally, the Low Power
Control (LPC) Register must be configured with 0xx0 data
(bits LX2HS and HSAUTO are set to 0).
SPI WAKE-UP
The sensitivity of the L0:L3 inputs is selected by the WUR
register. Level sensitivity is configured by L0:L3 input pairs:
L0 and L1 level sensitivity are configured together, while L2
and L3 are configured together.
The 33742 can be awakened by changes on the CS pin in
Sleep or Stop modes. Wake-up is detected as a LOW-to-
HIGH level transition on the CS pin. In the Stop mode, this
corresponds to a condition where an MCU and the SBC are
both in the Stop mode and when the application wake-up
event comes through the MCU.
CYCLIC SENSE WAKE-UP (CYCLIC SENSE TIMER
AND WAKE-UP INPUTS L0:L3)
33742 POWER-UP AND WAKE-UP FROM SLEEP
MODE
The 33742 can wake up upon state change of one of the
four wake-up input lines (L0:L3). The external pullup or pull-
down resistor of the switches associated with the wake-up
input lines can be biased from the HS VSUP switch. The HS
switch is activated in Sleep or Stop modes from an internal
timer. Cyclic Sense and Forced Wake-Up are exclusive
states. If Cyclic Sense is enabled, Forced Wake-Up cannot
be enabled.
After device or system power-up, or after the SBC
awakens from Sleep mode, the 33742S enters into the Reset
mode prior to moving into Normal Request mode.
Figure 13, shows the device state diagram. Figure 14,
shows device operation after power-up.
33742
Analog Integrated Circuit Device Data
Freescale Semiconductor
28
FREESCALE [ Freescale ]
