ST72321B STMICROELECTRONICS [STMicroelectronics], ST72321B Datasheet - Page 28

• Manufacturer Part Number: ST72321B
• Description: 64/44-pin 8-bit MCU with 32 to 60K Flash/ROM, ADC, five timers, SPI, SCI, I2C interface
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

6.4 SYSTEM INTEGRITY MANAGEMENT (SI)
The System Integrity Management block contains
the Low Voltage Detector (LVD), Auxiliary Voltage
Detector (AVD) functions. It is managed by the
SICSR register.
6.4.1 Low Voltage Detector (LVD)
The Low Voltage Detector function (LVD) gener-
ates a static reset when the V
below a V
secures the power-up as well as the power-down
keeping the ST7 in reset.
The V
than the V
to avoid a parasitic reset when the MCU starts run-
ning and sinks current on the supply (hysteresis).
The LVD Reset circuitry generates a reset when
V
The LVD function is illustrated in
The voltage threshold can be configured by option
byte to be low, medium or high.
Provided the minimum V
the oscillator frequency) is above V
can only be in two modes:
Figure 16. Low Voltage Detector vs Reset
28/187
DD
– V
– V
RESET
is below:
IT-
IT+
IT-
V
V
reference value for a voltage drop is lower
when V
when V
IT-
IT+
IT+
IT-
reference value for power-on in order
reference value. This means that it
V
DD
DD
DD
is falling
is rising
DD
value (guaranteed for
DD
Figure
supply voltage is
IT-
, the MCU
16.
In these conditions, secure operation is always en-
sured for the application without the need for ex-
ternal reset hardware.
During a Low Voltage Detector Reset, the RESET
pin is held low, thus permitting the MCU to reset
other devices.
Notes:
The LVD allows the device to be used without any
external RESET circuitry.
If the medium or low thresholds are selected, the
detection may occur outside the specified operat-
ing voltage range. Below 3.8V, device operation is
not guaranteed.
The LVD is an optional function which can be se-
lected by option byte.
It is recommended to make sure that the V
ply voltage rises monotonously when the device is
exiting from Reset, to ensure the application func-
tions properly.
V
– under full software control
– in static safe reset
hys
DD
sup-