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S39454B/F9454B
RESET and POWER-DOWN
8-1
8
RESET and POWER-DOWN
SYSTEM RESET
OVERVIEW
By smart option (3EH.7 in ROM), user can select internal RESET (LVR) or external RESET. In using internal
RESET (LVR), nRESET pin (P1.2) can be used by normal I/O pin.
The S3C9454B/F9454B can be RESET in four ways:
— by external power-on-reset
— by the external nRESET 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
DD
is High level and the nRESET pin is forced to Low level. The
nRESET signal is input through a Schmitt trigger circuit where it is then synchronized with the CPU clock. This
brings the S3C9454B/F9454B into a known operating status. To ensure correct start-up, the user should take care
that nRESET signal is not released before the V
DD
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 (@ 2
16/
f
OSC
, f
OSC
= 10 MHz).
When a reset occurs during normal operation (with both V
DD
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 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 RESET. The MCU can start
only when the supply voltage rises over the reference value.
Summary of Contents for S3C9454B
Page 1: ...S3C9454B F9454B 8 BIT CMOS MICROCONTROLLER USER S MANUAL Revision 1 ...
Page 25: ...PRODUCT OVERVIEW S3C9454B F9454B 1 10 NOTES ...
Page 35: ...ADDRESS SPACES S3C9454B F9454B 2 10 NOTES ...
Page 65: ...CONTROL REGISTERS S3C9454B F9454B 4 18 NOTES ...
Page 123: ...CLOCK CIRCUIT S3C9454B F9454B 7 4 NOTES ...
Page 133: ...RESET and POWER DOWN S39454B F9454B 8 10 NOTES ...
Page 145: ...I O PORTS S3C9454B F9454B 9 12 NOTES ...
Page 173: ...A D CONVERTER S3C9454B F9454B 12 8 NOTES ...
Page 183: ...ELECTRICAL DATA S3C9454B F9454B 13 10 NOTES ...