mc33789 Freescale Semiconductor, Inc, mc33789 Datasheet - Page 41

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

Watchdog Error
Arm Lockout and WDOG_TEST
outputs are forced to the high-impedance state, which is
called Arm Lockout. To individually test ARM and DISARM
(The tests allow both the ARM and DISARM pins to be set to
“1” or “0” at same time) while the WSM is still running in the
background, the WSM can be set to the WDOG OVERRIDE
state after a WSM reset, or insert the SPI command of
WDOG_TEST from the DRIVE state, to avoid setting
ARM_LOCKOUT = 1.
which can be measured at the RESET pin and can be
checked by using the SPI STATUS command to read the bit
WDR = 1, it does not always cause an Arm Lockout, which
depends on the WSM running in the DRIVE state, or in the
WDOG TEST state before the watchdog error occurs.
Regardless whether the watchdog error causes an Arm
Analog Integrated Circuit Device Data
Freescale Semiconductor
WDOG Error is defined as:
WDOG Refresh OK is defined as:
During a system reset, both the ARM and DISARM pin
Though watchdog error always causes a system reset,
WDOG_FEED before the min. window time to the
NOT [WDOG OVERIDE]
AND
[WDOG_FEED with same polarity as the previous feed
OR
previous feed
OR
WDOG_FEED after the max. window time to the
previous feed]
WDOG_FEED with opposite polarity to the previous feed
WDOG RESET
1.0 ms
WDOG error
Set WDR = 1
WSM_Reset
(From any state)
Set ARM_LOCKOUT = 0
Set WDR = 0
WDOG error
Set WDR = 1
Set ARM_LOCKOUT = 1
WDOG error
Set WDR = 1
Set ARM_LOCKOUT = 1
Figure 36. Watchdog State Diagram
WDOG refresh OK
INITIAL
pulled down for 1.0 ms to reset the system, and the 33789
internal status register will set the Watchdog Error Status bit
WDR = 1, to indicate a watchdog error is the source of the
reset.
MCU via the SPI STATUS request command. The WDR bit is
cleared by either a WSM_Reset or a correct WDOG_FEED.
Lockout, the WSM_Reset always brings the WSM back to the
INITIAL state, with the setting of ARM_LOCKOUT = 0 and
WDR = 0 at the end of the system reset.
command WDOG_TEST can be used to prevent the Arm
Lockout caused by a watchdog error. This command is only
valid for the next watchdog window: A WDOG_TEST
command has to be inserted before a watchdog error (invalid
refresh or missing refresh) within the same watchdog
window. Thus, once the error occurs, the consequential
resets would not cause an Arm Lockout. (See
some typical examples of successful and unsuccessful
inserted SPI WDOG_TEST commands)
WDOG TEST
DRIVE
If a window watchdog refresh fails, the RESET pin will be
The value of the WDR bit is latched and can be read by the
To facilitate testing of the watchdog error function, the SPI
feed
previous feed
AND
WDOG_FEED after the min. window time to the previous
AND
WDOG_FEED before the max. window time to the
WDOG refresh OK
Set WDR = 0
SPI WDOG_TEST
V
AND
SPI WDOG_TEST
PPT
>V
WDOG refresh OK
PPT_TEST
FUNCTIONAL DEVICE OPERATION
WDOG OVERRIDE
OPERATING MODES
Figure 37
33789
for
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