S3C84E5/C84E9/P84E9 LOW VOLTAGE RESET
16-1
16 LOW VOLTAGE RESET
OVERVIEW
The S3C84E5/C84E9/P84E9 can be reset in four ways:
— by external power-on-Reset
— by the external nReset input pin pulled low
— by the digital watchdog timing out
— by the Low Voltage reset circuit (LVR)
During an external power-on reset, the voltage VDD is High level and the nRESET pin is forced Low level. The
RESET signal is input through a Schmitt trigger circuit where it is then synchronized with the CPU clock. This brings
the S3C84E5/C84E9/P84E9 into a known operating status. To ensure correct start-up, the user should take that
Reset signal is not released before the VDD level is sufficient to allow MCU operation at the chosen frequency.
The nRESET 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 stabilization
time for a Reset is approximately 6.55 ms (≅216/fosc, fosc = 10MHz).
When a Reset occurs during normal operation (with both VDD and nRESET at High level), the signal at the nRESET
pin is 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 S3C84E5/C84E9/P84E9 has a built-in low voltage Reset circuit that allows detection of power voltage drop of
external VDD input level to prevent a MCU from malfunctioning in an unstable MCU power level. This voltage detector
works for the Reset operation of MCU. This Low Voltage reset includes an analog compactor and Vref circuit. The
value of a detection voltage is set internally by hardware. The on-chip Low Voltage Reset, features static reset when
supply voltage is below a reference voltage value (Typical 2.9 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 an
internal and static RESET. The MCU can start only when the supply voltage rises over the reference voltage.
When you calculate power consumption, please remember that a static current of LVR circuit should be added a
CPU operating current in any operating modes such as Stop, Idle, and normal RUN mode.