ST72F321J ST Microelectronics, ST72F321J Datasheet - Page 27

• Manufacturer Part Number: ST72F321J
• Description: 8-BIT MCU
• Manufacturer: ST Microelectronics

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DataSheet
SYSTEM INTEGRITY MANAGEMENT (Cont’d)
6.4.2 Auxiliary Voltage Detector (AVD)
The Voltage Detector function (AVD) is based on
an analog comparison between a V
V
ply. The V
lower than the V
age in order to avoid parasitic detection (hystere-
sis).
The output of the AVD comparator is directly read-
able by the application software through a real
time status bit (AVDF) in the SICSR register. This
bit is read only.
Caution: The AVD function is active only if the
LVD is enabled through the option byte.
6.4.2.1 Monitoring the V
The AVD voltage threshold value is relative to the
selected LVD threshold configured by option byte
(see
If the AVD interrupt is enabled, an interrupt is gen-
erated when the voltage crosses the V
V
Figure 14. Using the AVD to Monitor V
IT+(AVD)
IT-(AVD)
AVDF bit
AVD INTERRUPT
REQUEST
IF AVDIE bit = 1
LVD RESET
4
V
V
V
Section 14.1 on page
V
IT+(AVD)
IT+(LVD)
IT-(LVD)
U
IT-(AVD)
.com
threshold (AVDF bit toggles).
reference value and the V
IT-
reference value for falling voltage is
V
DD
IT+
reference value for rising volt-
0
DD
169).
Main Supply
1
DD
INTERRUPT PROCESS
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IT-(AVD)
IT+(AVD)
main sup-
V
Early Warning Interrupt
(Power has dropped, MCU not
not yet in reset)
DD
hyst
RESET VALUE
and
or
In the case of a drop in voltage, the AVD interrupt
acts as an early warning, allowing software to shut
down safely before the LVD resets the microcon-
troller. See
The interrupt on the rising edge is used to inform
the application that the V
If the voltage rise time t
CPU cycles (depending on the reset delay select-
ed by option byte), no AVD interrupt will be gener-
ated when V
If t
– If the AVD interrupt is enabled before the
– If the AVD interrupt is enabled after the V
V
rupts will be received: the first when the AVDIE
bit is set, and the second when the threshold is
reached.
threshold is reached then only one AVD interrupt
will occur.
rv
IT+(AVD)
is greater than 256 or 4096 cycles then:
threshold is reached, then 2 AVD inter-
Figure
IT+(AVD)
t
1
14.
rv
VOLTAGE RISE TIME
is reached.
rv
DD
is less than 256 or 4096
warning state is over.
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INTERRUPT PROCESS
0
ST72321J
IT+(AVD)
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