ST72T331 STMICROELECTRONICS [STMicroelectronics], ST72T331 Datasheet - Page 20

• Manufacturer Part Number: ST72T331
• Description: 8-BIT MCU WITH 8 TO 16K OTP/EPROM, 256 EEPROM, 384 TO 512 BYTES RAM, ADC, WDG, SCI, SPI AND 2 TIMERS
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

ST72E331 ST72T331
RESET (Cont’d)
3.2.4 Low Voltage Detector Reset
The on-chip Low Voltage Detector (LVD) gener-
ates a static reset when the supply voltage is be-
low a reference value. The LVD functions both
during power-on as well as when the power supply
drops (brown-out). The reference value for a volt-
age drop is lower than the reference value for pow-
er-on in order to avoid a parasitic reset when the
MCU starts running and sinks current on the sup-
ply (hysteresis).
The LVD Reset circuitry generates a reset when
V
Provided the minimun V
the oscillator frequency) is above V
MCU can only be in two modes:
- under full software control or
- in static safe reset
In this condition, 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.
In noisy environments, the power supply may drop
for short periods and cause the Low Voltage De-
tector to generate a Reset too frequently. In such
Figure 16. Temporization timing diagram after an internal Reset
20/107
20
DD
V
V
LVDUP
LVDDOWN
is below:
when V
when V
V
Addresses
DD
DD
is rising
DD
is falling
DD
value (guaranteed for
V
LVDUP
LVDDOWN
Temporization (4096 CPU clock cycles)
, the
$FFFE
cases, it is recommended to use devices without
the LVD Reset option and to rely on the watchdog
function to detect application runaway conditions.
Figure 14. Low Voltage Detector Reset Function
Figure 15. Low Voltage Detector Reset Signal
Note: See electrical characteristics for values of
V
RESET
LVDUP
V
V
DD
DD
V
and V
LVDUP
DETECTOR RESET
LOW VOLTAGE
LVDDOWN
WATCHDOG
RESET
FROM
V
LVDDOWN
RESET