参数资料
型号: ST6246B
英文描述: 8-BIT MICROCONTROLLER ( MCU ) WITH OTP. ROM. FASTROM. EPROM. LCD DRIVER. EEPROM. A/D CONVERTER AND 56 PINS
中文描述: 8位微控制器(MCU)的与检察官办公室。光盘。 FASTROM。存储器。液晶显示驱动程序。 EEPROM中。的A / D转换器和56图钉
文件页数: 20/74页
文件大小: 733K
代理商: ST6246B
20/74
ST62T46B/E46B
3.2 RESETS
The MCU can be reset in three ways:
– by the external Reset input being pulled low;
– by Power-on Reset;
– by the digital Watchdog peripheral timing out.
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
DD
has
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 at an appropriate stage during the
power-on sequence. At the beginning of this se-
quence, 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 executing the first instruction.
The initialization sequence is executed immediate-
ly following the internal delay.
The internal delay is generated by an on-chip coun-
ter. The internal reset line is released 2048 internal
clock cycles after release of the external reset.
Notes:
To ensure correct start-up, the user should take
care that the reset signal is not released before the
V
DD
level is sufficient to allow MCU operation at
the chosen frequency (see Recommended Oper-
ating Conditions).
A proper reset signal for a slow rising V
DD
supply
can generally be provided by an external RC net-
work connected to the RESET pin.
Figure 11. Reset and Interrupt Processing
INNMI MASK SET
( IF PRESENT )
RESET
SELECT
NMI MODE FLAGS
IS RESET STILL
PRESENT
YES
PUT FFEH
ON ADDRESS BUS
FROM RESET LOCATIONS
FFE/FFF
NO
FETCH INSTRUCTION
LOAD PC
VA000427
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