st62t62cmae STMicroelectronics, st62t62cmae Datasheet - Page 21

• Manufacturer Part Number: st62t62cmae
• Description: 8-bit Otp/eprom/fastrom Mcus With A/d Converter, Safe Reset, Auto-reload Timer And Eeprom
• Manufacturer: STMicroelectronics

3.2 RESETS
The MCU can be reset in four ways:
– by the external Reset input being pulled low;
– by Power-on Reset;
– by the digital Watchdog peripheral timing out.
– by Low Voltage Detection (LVD)
3.2.1 RESET Input
The RESET pin may be connected to a device of
the application board in order to reset the MCU if
required. The RESET pin may be pulled low in
RUN, WAIT or STOP mode. This input can be
used to reset the MCU internal state and ensure a
correct start-up procedure. The pin is active low
and features a Schmitt trigger input. The internal
Reset signal is generated by adding a delay to the
external signal. Therefore even short pulses on
the RESET pin are acceptable, provided V
completed its rising phase and that the oscillator is
running correctly (normal RUN or WAIT modes).
The MCU is kept in the Reset state as long as the
RESET pin is held low.
If RESET activation occurs in the RUN or WAIT
modes, processing of the user program is stopped
(RUN mode only), the Inputs and Outputs are con-
figured as inputs with pull-up resistors and the
main Oscillator is restarted. When the level on the
RESET pin then goes high, the initialization se-
quence is executed following expiry of the internal
delay period.
If RESET pin activation occurs in the STOP mode,
the oscillator starts up and all Inputs and Outputs
are configured as inputs with pull-up resistors.
When the level of the RESET pin then goes high,
the initialization sequence is executed following
expiry of the internal delay period.
3.2.2 Power-on Reset
The function of the POR circuit consists in waking
up the MCU by detecting around 2V a dynamic
(rising edge) variation of the VDD Supply. At the
beginning of this sequence, the MCU is configured
in the Reset state: all I/O ports are configured as
inputs with pull-up resistors and no instruction is
executed. When the power supply voltage rises to
a sufficient level, the oscillator starts to operate,
whereupon an internal delay is initiated, in order to
allow the oscillator to fully stabilize before execut-
ing the first instruction. The initialization sequence
DD
has
is executed immediately following the internal de-
lay.
To ensure correct start-up, the user should take
care that the VDD Supply is stabilized at a suffi-
cient level for the chosen frequency (see recom-
mended operation) before the reset signal is re-
leased. In addition, supply rising must start from
0V.
As a consequence, the POR does not allow to su-
pervise static, slowly rising, or falling, or noisy
(presenting oscillation) VDD supplies.
An external RC network connected to the RESET
pin, or the LVD reset can be used instead to get
the best performances.
Figure 13. Reset and Interrupt Processing
ST62T52CM-Auto ST62T62CM-Auto
YES
FROM RESET LOCATIONS
FETCH INSTRUCTION
INT LATCH CLEARED
ON ADDRESS BUS
NMI MODE FLAGS
IS RESET STILL
( IF PRESENT )
NMI MASK SET
PUT FFEH
LOAD PC
PRESENT?
SELECT
FFE/FFF
RESET
NO
VA000427
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