mc33789 Freescale Semiconductor, Inc, mc33789 Datasheet - Page 40

• Manufacturer Part Number: mc33789
• Description: Airbag System Basis Chip Sbc With Power Supply And Psi5 Sensor Interface
• Manufacturer: Freescale Semiconductor, Inc

FUNCTIONAL DEVICE OPERATION
OPERATING MODES
Start-up Behavior
supply holds the RESET pin low and keeps the watchdog in
a “INITIAL” state with the 33789 status register bit WDR = 0,
which indicates the reset is not caused by any watchdog
error. The register is guaranteed by design to be inactive
during the V
entered into the valid voltage range, the RESET pin is
released and the system operation starts.
40
33789
The functions of the reset signals are:
• Internal_Reset: Resets all internal blocks except Safing
• WSM_Reset: Resets Watchdog State Machine
• SSM_Reset: Resets Safing State Machine
• Analog_Reset: Arm enable for ARM / DISARM
• Sleep_Reset: Resets Sleep_Mode Logic
After wake-up, when V
When the power-on delay has elapsed and V
Band gap V
and Watchdog
Ba ndg ap_OK
WDOG Er ror
WDOG Test
GNDA Lo ss
CC
V
V
V
V
R EF
CC
CC
D D
D D
ramp up period.
_OK
_OV
_UV
_ UV
_OV
Refr esh
WDOG
CC
ramps up, the internal power
Refresh
Last
t
WD W_MIN
t
WDW_MAX
Acceptance
Refresh
W indow
Figure 35. Watchdog Windows
CC
has
Figure 34. Reset Logic
Watchdog
Window
(WDW)
t
Delay
Delay
10 ms
1ms
operation until the first watchdog feed command is received.
outputs are forced to maintain their high-impedance states.
Watchdog Window
two adjacent watchdog refreshes. The 33789 uses software
watchdog, it periodically receives watchdog refresh signals
from the MCU through the SPI interface.
WDOG_FEED (high or low), followed by another SPI
command, WDOG_FEED (low or high), within a designated
watchdog window. (See
command, the first successful refresh occurs and the
watchdog transits from “INITIAL” state to “DRIVE” state. (See
Figure
The Watchdog State machine (WSM) does not start its
Before the first watchdog refresh, the ARM and DISARM
A watchdog window is defined as a time window between
A successful watchdog refresh is a SPI command,
Once the 33789 receives the first WDOG_FEED
Refresh
WDOG
36, Watchdog State Diagram)
Refresh
Last
t
W DW_MIN
t
WDW_M AX
Acceptance
Analog Integrated Circuit Device Data
Window
Refresh
Figure
35, Watchdog Windows)
Freescale Semiconductor
t
SSM_Reset
Slee p_ Rese t
Inte rnal_Re set
WSM_Reset
Anal og_Reset
RESET