SN32F280 Series
32-Bit Cortex-M0 Micro-Controller
SONiX TECHNOLOGY CO., LTD
Page 49
Version 1.1
3.1.2 WATCHDOG RESET (WDT RESET)
Watchdog reset is a system protection. In normal condition, system works well and clears watchdog timer by program.
Under error condition, system is in unknown situation and watchdog c
an’t be clear by program before watchdog timer
overflow. Watchdog timer overflow occurs and the system is reset. After watchdog reset, the system restarts and returns
normal mode. Watchdog reset sequence is as following.
Watchdog timer status:
System checks watchdog timer overflow status. If watchdog timer overflow occurs, the
system is reset.
System initialization:
All system registers is set as initial conditions and system is ready.
Oscillator warm up:
Oscillator operation is successfully and supply to system clock.
Program executing:
Power on sequence is finished and program executes from Boot loader if BLEN bit =1, or
from 0x0 if BLEN bit =0.
Watchdog timer application note is as following.
Before clearing watchdog timer, check I/O status and check RAM contents can improve system error.
Don’t clear watchdog timer in interrupt vector and interrupt service routine. That can improve main routine fail.
Clearing watchdog timer program is only at one part of the program. This way is the best structure to enhance the
watchdog timer function.
Note: Please refer to the “WATCHDOG TIMER” about watchdog timer detail information.
3.1.3 BROWN-OUT RESET
3.1.3.1
BROWN OUT DESCRIPTION
The brown-out reset is a power dropping condition. The power drops from normal voltage to low voltage by external
factors (e.g. EFT interference or external loading changed). The brown out reset would make the system not work well
or executing program error.
VDD
VSS
V1
V2
V3
System Work
Well Area
System Work
Error Area
Brown-Out Reset Diagram
The power dropping might through the voltage range that’s the system dead-band. The dead-band means the power
range can’t offer the system minimum operation power requirement. The above diagram is a typical brown out reset
diagram. There is a serious noise under the VDD, and VDD voltage drops very deep. There is a dotted line to separate
the system working area. The above area is the system work well area. The below area is the system work error area
called dead-
band. V1 doesn’t touch the below area and not affect the system operation. But the V2 and V3 is under the
below area and may induce the system error occurrence. Let system under dead-band includes some conditions.
DC application:
The power source of DC application is usually using battery. When low battery condition and MCU drive any loading, the
power drops and keeps in dead-
band. Under the situation, the power won’t drop deeper and not touch the system reset
voltage. That makes the system under dead-band.
