TC1784
System Control Unit (SCU)
User´s Manual
3-137
V1.1, 2011-05
32-bit SCU, V1.18
WDT_CON0. Instead of immediately requesting a reset of the device, the WDT enables
the system to enter a secure state by a prewarning before the reset occurs.
In Prewarning Mode, after having generated the NMI request, the WDT counts up from
FFFC
H
, and then generates a Watchdog reset request on the overflow. This reset
request cannot be avoided in this mode; the WDT does not react anymore to accesses
to its registers, nor will it change its state unless reset by an Application Reset. This is to
prevent a malfunction from falsely terminating this mode, disabling the reset, and letting
the device to continue to function improperly. Register WDT_CON0 can still be accessed
by a valid Password Access.
Note: In Prewarning Mode, it is not required for the part to wait for the end of this mode
and the reset. After having saved required state in the NMI routine, software can
execute an Application Reset to shorten the time.
Note: The Prewarning Mode is only left by an application Reset and not only on the reset
request. Therefore if bit field RSTCON.WDT is set to 00
B
the Prewarning Mode is
not left.
3.8.4.2
WDT Reset Behavior
WDT reset requests are generated for three cases:
•
Invalid password access to register WDT_CON0
•
Not finishing a password access before a timer overflow occurs in the Time-Out
Mode
•
Not serving the WDT before a timer overflow occurs in the Normal Mode
If a reset is generated on a WDT reset request and the kind of the reset can be
configured via bit field RSTCON.WDT.
Note: The WDT itself is reset by any Application Reset.
Before a reset is requested the Prewarning Mode is entered, for more details see
Double WDT Reset
If the Watchdog induced reset occurs twice, a severe system malfunction is assumed
and the TC1784 is held in reset until a System Reset occurs. This prevents the device
from being periodically reset if, for instance, connection to the external memory has been
lost such that even system initialization could not be performed.
If the WDT is configured to request an Application Reset the second reset request will
be permanently asserted resulting (without any change in the reset configuration)
resulting in a permanent Application Reset. The information about the first WDT reset
request is stored in an internal flag which is reset with the System Reset. This flag is set
when the Prewarning Mode is finished and the reset request is generated. If a new reset
is requested and the internal flag is already set a double reset event has occurred and a
Summary of Contents for TC1784
Page 1: ...User s Manual V1 1 2011 05 Microcontrollers TC1784 32 Bit Single Chip Microcontroller ...
Page 3: ...User s Manual V1 1 2011 05 Microcontrollers TC1784 32 Bit Single Chip Microcontroller ...
Page 950: ...TC1784 Direct Memory Access Controller DMA User s Manual 11 132 V1 1 2011 05 DMA V3 03 ...
Page 1949: ...TC1784 General Purpose Timer Array GPTA v5 User s Manual 21 297 V1 1 2011 05 GPTA v5 V1 14 ...
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