The effect on the WDT for each of these system
events may be individually enabled or disabled
through bits in the WDT_CFG configuration
register. When a system event is enabled
through the WDT_CFG register, the occurrence
of that event will cause the WDT to reload the
value stored in WDT_VAL and reset the WDT
time-out status bit if set. If all three system
events are disabled the WDT will inevitably time
out.
The host may force a Watch Dog time-out to
occur by writing a "1" to bit 2 of the WDT_CTRL
(Force WD Time-out) Configuration Register.
Writing a "1" to this bit forces the WDT count
value to zero and sets bit 0 of the WDT_CTRL
(Watch Dog Status). Bit 2 of the WDT_CTRL is
self-clearing.
Power LED Toggle
Setting bit 1 of the WDT_CTRL Configuration
Register will cause the power LED output driver
to toggle at 1 Hertz with a 50 percent duty cycle.
When this bit is cleared the Power LED output
will drive continuously unless it has been
configured to toggle on Watch Dog time-out
conditions. Setting bit 3 of the WDT_CFG
Configuration Register will cause the Power LED
output driver to toggle at 1 Hertz with a 50
percent duty cycle whenever the WDT time-out
status bit is set. The truth table below clarifies
the conditions for which the power LED will
toggle.
The Watch Dog Timer may be configured to
generate an interrupt on the rising edge of the
time-out status bit.
mapped to an interrupt channel through the
WDT_CFG Configuration Register. When
The WDT interrupt is
mapped to an interrupt the interrupt request pin
reflects the value of the WDT time-out status bit.
When the polarity bit is 0, GP12 reflect the value
of the Watch Dog Time-out status bit, however,
when the polarity bit is 1, GP12 reflects the
inverted value of the Watch Dog Time-out status
bit. This is also true for the other two pins used
for WDT; nIOROP (GP46) and RD1 (GP61).
When the polarity bit is 0, the power LED output
asserts or drives low. If the polarity bit is 1 then
the power LED output asserts or drives high.
Table 54 - LED Toggle Truth Table
WDT_CFG BIT 3
POWER LED
WDT_CTRL BIT 1
WDT_CTRL BIT 0
POWER LED TOGGLE
TOGGLE ON WDT
POWER LED STATE
Toggle
WDT T/O STATUS BIT
1
0
0
0
X
0
1
1
X
X
0
1
Continuous
Continuous
Toggle
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