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TC1796
System Units (Vol. 1 of 2)
Watchdog Timer
User’s Manual
16-13
V2.0, 2007-07
WDT, V2.0
16.4.6
Detailed Descriptions of the WDT Modes
The following subsections provide detailed descriptions of each of the modes of the
WDT. The entry conditions and actions, operation in this mode, as well as exit conditions
and the succeeding mode are listed for each mode.
16.4.6.1 Time-Out Mode Details
Time-Out Mode is the default after reset, and is entered each time a Valid Password
Access to register WDT_CON0 is performed.
Table 16-4
WDT Time-Out Mode
State /
Action
Description
Entry
•
Automatically after any reset
•
If a valid password was written to WDT_CON0 in Normal or Disable
Mode
Actions
on Entry
•
WDTTIM is set to FFFC
H
; WDTTO is set to 1; WDTDS is set to 0.
•
ENDINIT = 0 if mode entered through reset; otherwise, it retains its
previous value.
•
Bits WDTAE and WDTOE depend on their state before the reset if the
reset was caused by the Watchdog. For any other reset (PORST,
HDRST, SRST, PWDRST), they are 0.
•
WDTIS retains its previous value.
•
After reset, ENDINIT is 0. Thus, access to Endinit-protected registers
is enabled. If Time-Out Mode was entered through other reasons,
ENDINIT might or might not be 0.
Operation
•
Timer starts counting up from FFFC
H
; increments with clock rate
determined through WDTIS (0 after reset, slowest clock).
•
Access to registers WDT_CON0 is possible. Access to register
WDT_CON1 is possible if ENDINIT = 0.
•
Restarting Time-Out Mode is not possible: A Valid Password Access in
this mode does not invoke another Time-out sequence (it does not
reload the timer, etc.). A Modify Access to WDT_CON0 writing a 0 to
ENDINIT does not terminate Time-Out Mode.
•
It is not possible to change the reload value or frequency in Time-Out
Mode, as this would require setting ENDINIT to 1, which terminates
Time-Out Mode. Reload value is not used until Normal Mode is
entered.