TC1784
System Control Unit (SCU)
User´s Manual
3-135
V1.1, 2011-05
32-bit SCU, V1.18
3.8.3.3
Access to Endinit-Protected Registers
If some or all of the system’s Endinit-protected registers must be changed during run
time of an application, access can be re-opened. To do this, WDT_CON0 must first be
unlocked with a Valid Password Access. In the subsequent Valid Modify Access,
ENDINIT can be cleared. Access to Endinit-protected registers is now open again.
However, when WDT_CON0 is unlocked, the WDT is automatically switched to Time-
Out Mode. Thus, the access window is time-limited. Time-Out Mode is only terminated
after ENDINIT has been set again, requiring another Valid Password and Valid Modify
Access to WDT_CON0.
If the WDT is not used in an application and is therefore disabled (WDT_SR.DS = 1), the
above described case is the only occasion when WDT_CON0 must be accessed again
after the system is initialized. If there are no further changes to critical system registers
needed, no further accesses to WDT_CON0, WDT_CON1, or WDT_SR are necessary.
However, it is recommended that the WDT be used in an application for safety reasons.
For debugging support the Cerberus module can override the ENDINIT control to ease
the debug flow. If bit CBS_OSTATE.ENIDIS is set the ENDINIT protection is disabled
independent of the current status configured by the WDT. If CBS_OSTATE.ENIDIS is
cleared the complete control is within the WDT.
3.8.4
Timer Operation
The timer is automatically active after an Application Reset. The 16-bit counter
implementing the timer functionality is either triggered with
f
FPI
/ 256 or
f
FPI
/ 16384. The
two possible counting rates are controlled via bit WDT_CON1.IR.
Determining WDT Periods
The WDT uses the FPI-Bus clock
f
FPI
. A clock divider in front of the WDT provides two
output frequencies,
f
FPI
/ 256 and
f
FPI
/ 16384.
The general formula to calculate a Watchdog period is:
(3.19)
The parameter start value represents the fixed value FFFC
H
for the calculation of the
Time-Out Period, and the user-programmable reload value WDT_CON0.REL for the
calculation of the Normal Period.
3.8.4.1
Timer Modes
The Watchdog Timer can operate in one of four different operating modes:
•
Time-Out Mode
period
2
16
startvalue
–
(
)
256 2
1 IR
–
(
)
6
⋅
⋅
⋅
f
FPI
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Summary of Contents for TC1784
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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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