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TC1784
System Control Unit (SCU)
User´s Manual
3-138
V1.1, 2011-05
32-bit SCU, V1.18
permanent request is generated. This internal flag is cleared by any System Reset or
when bit WDT_CON1.CLRIRF is set AND bit WDT_CON0.ENDINIT is set too. Please
note that a correct service of the WDT does not clear this internal flag. Bit
WDT_CON1.CLRIRF can only be set when bit WDT_CON0.ENDINIT is cleared.
Note: It does not matter whether a reset was generated on a WDT reset request or if the
reset configuration was changed between the two reset requests.
Note: If for any reason random code is executed bit field RSTCON.WDT can be updated
unintentional. This can result that a WDT error does not lead to an reset. To avoid
this after the SSW is finished this bit field should be checked and the ENDINIT
protection enabled.
Servicing the Watchdog Timer
If the WDT is used in an application and is enabled (WDT_SR.DS = 0), it must be
regularly serviced to prevent it from overflowing.
Service is performed in two steps. a Valid Password Access followed by a Valid Modify
Access. The Valid Password Access to WDT_CON0 automatically switches the WDT to
Time-Out Mode. Thus, the Modify Access must be performed before the Time-out
expires or a System Reset will result.
During the next Modify Access, the strict requirement is that WDT_CON0.ENDINIT as
well as bit 1 and bits [7:4] are written with 1, while bits [3:2] are written with 0.
Note: ENDINIT must be written with 1 to perform a proper service, even if it is already
set to 1.
Changes to the reload value WDT_CON0.REL, or the user-definable password
WDT_CON0.PW, are not required. However, changing WDT_CON0.PW is
recommended so that software can monitor WDT service operations throughout the
duration of an application program (see next section).
When WDT service is properly executed, Time-Out Mode is terminated, and the WDT
switches back to its former mode of operation, and WDT service is complete.
3.8.4.3
WDT Operation During Power-Saving Modes
If the CPU is in Idle Mode or Sleep Mode, it cannot service the WDT because no software
is running. Excluding the case where the system is running normally, a strategy for
managing the WDT is needed while the CPU is in Idle or Sleep Mode. There are two
ways to manage the WDT in these cases. First, the Watchdog can be disabled before
idling the CPU. The disadvantage of this is that the system will no longer be monitored
during the idle period.
A better approach to this problem relies upon a wake-up feature of the WDT. Whenever
the CPU is put in Idle or Sleep Mode and the WDT is not disabled, it causes the CPU to
be awakened at regular intervals. When the WDT changes its count value
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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