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SPECIAL OPERATING MODES
When using an external interrupt signal to exit powerdown mode, we recommend that you con-
nect the external RC circuit shown in Figure 13-3 to the V
pin. The discharging of the capacitor
PP
causes a delay that allows the oscillator to stabilize before the internal CPU and peripheral clocks
are enabled.
V CC
8XC196
Device
R 1 1 MΩ Typical
V PP
C 1 1µF Typical
A0279-01
Figure 13-3. External RC Circuit
During normal operation (before entering powerdown mode), an internal pull-up holds the
V
pin at V
. When an external interrupt signal is asserted, the internal oscillator circuitry is
PP
CC
enabled and turns on a weak internal pull-down. This weak pull-down causes the external capac-
) to begin discharging at a typical rate of 200 µA. When the V
itor (C
pin voltage drops below
1
PP
the threshold voltage (about 2.5 V), the internal phase clocks are enabled and the device resumes
code execution.
At this time, the internal pull-up transistor turns on and quickly pulls the pin back up to about
3.5 V. The pull-up becomes ineffective and the external resistor (R
) takes over and pulls the volt-
1
age up to V
(see recovery time in Figure 13-4). The time constant follows an exponential charg-
CC
= 1 µF and R
ing curve. If C
= 1 MΩ, the recovery time will be one second.
1
1
13.4.3.4
Selecting R
and C
1
1
The values of R
and C
are not critical. Select components that produce a sufficient discharge
1
1
time to permit the internal oscillator circuitry to stabilize. Because many factors can influence the
discharge time requirement, you should always fully characterize your design under worst-case
conditions to verify proper operation.
13-7
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