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S3C9442/C9444/F9444/C9452/C9454/F9454
and POWER-DOWN
RESET
8
and POWER-DOWN
RESET
SYSTEM RESET
OVERVIEW
By smart option (3EH.7 in ROM), user can select internal
(LVR) or external
. In using internal
RESET
RESET
(LVR),
pin (P1.2) can be used by normal I/O pin.
RESET
RESET
The S3C9442/C9444/C9452/C9454 can be
in four ways:
RESET
— by external power-on-reset
— by the external reset input pin pulled low
— by the digital watchdog peripheral timing out
— by Low Voltage reset (LVR)
During a external power-on reset, the voltage at V
is High level and the
pin is forced to Low level. The
DD
signal is input through a Schmitt trigger circuit where it is then synchronized with the CPU clock. This brings
the S3C9442/C9444/C9452/C9454 into a known operating status. To ensure correct start-up, the user should take
care that reset signal is not released before the V
level is sufficient to allow MCU operation at the chosen
DD
frequency.
The
pin must be held to Low level for a minimum time interval after the power supply comes within
tolerance in order to allow time for internal CPU clock oscillation to stabilize. The minimum required oscillation
16 /
stabilization time for a reset is approximately 6.55 ms (≅ 2
f
, f
= 10 MHz).
OSC
OSC
When a reset occurs during normal operation (with both V
and
at High level), the signal at the
pin is
DD
forced Low and the reset operation starts. All system and peripheral control registers are then set to their default
hardware reset values (see Table 8-1).
The MCU provides a watchdog timer function in order to ensure graceful recovery from software malfunction. If
watchdog timer is not refreshed before an end-of-counter condition (overflow) is reached, the internal reset will be
activated.
The on-chip Low Voltage reset, features static Reset when supply voltage is below a reference value (Typ. 2.3,
3.0, 3.9 V). Thanks to this feature, external reset circuit can be removed while keeping the application safety. As
long as the supply voltage is below the reference value, there is a internal and static
. The MCU can start
RESET
only when the supply voltage rises over the reference value.
8-1
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