SN32F280 Series
32-Bit Cortex-M0 Micro-Controller
SONiX TECHNOLOGY CO., LTD
Page 51
Version 1.1
LVD reset:
VDD
VSS
System Normal Run
System Stop
LVD Detect Voltage
Power On
Delay Time
Power
System Status
Power is below LVD Detect
Voltage and System Reset.
The LVD (low voltage detector) is built-in SONiX 32-bit MCU to be brown out reset protection. When the VDD drops and
is below LVD detect voltage, the LVD asserts an interrupt signal to the NVIC. This signal can be enabled for interrupt in
the Interrupt Enable Register in the NVIC in order to cause a CPU interrupt; if not, SW can monitor the signal by reading
a dedicated status register. An additional threshold level can be selected to cause a forced reset of the chip. The LVD
detect level is different by each MCU. The LVD voltage level is a point of voltage and not easy to cover all dead-band
range. Using LVD to improve brown out reset is dependent on application requirement and environment. If the power
variation is very deep, violent and trigger the LVD, the LVD can be the protection. If the power variation can touch the
LVD detect level and make system work error, the LVD can’t be the protection and need to other reset methods. More
detail LVD information is in the electrical characteristic section.
Watchdog reset:
The watchdog timer is a protection to make sure the system executes well. Normally the watchdog timer would be clear
at one point of program. Don’t clear the watchdog timer in several addresses. The system executes normally and the
watchdog won’t reset system. When the system is under dead-band and the execution error, the watchdog timer can’t
be clear by program. The watchdog is continuously counting until overflow occurrence. The overflow signal of watchdog
timer triggers the system to reset and return to normal mode after reset sequence. This method also can improve brown
out reset condition and make sure the system to return normal mode.
If the system reset by watchdog and the power is still in dead-
band, the system reset sequence won’t be successful and
the system stays in reset status until the power return to normal range.
Reduce the system executing rate:
If the system rate is fast and the dead-band exists, to reduce the system executing rate can improve the dead-band. The
lower system r
ate is with lower minimum operating voltage. Select the power voltage that’s no dead-band issue and find
out the mapping system rate. Adjust the system rate to the value and the system exits the dead-band issue. This way
needs to modify whole program timing to fit the application requirement.
External reset circuit:
The external reset methods also can improve brown out reset and is the complete solution. There are three external
reset circuits to improve brown out reset including “Zener diode reset circuit”, “Voltage bias reset circuit” and “External
reset IC”. These three reset structures use external reset signal and control to make sure the MCU be reset under power
dropping and under dead-band. The external reset information is described in the next section.
3.1.4 EXTERNAL RESET
External reset function is controlled by
External RESET pin control (SYS0_EXRSTCTRL)
which means external reset function is enabled. External reset pin is Schmitt Trigger structure and low level active. The
system is running when reset pin is high level voltage input. The reset pin receives the low voltage and the system is
reset. The external reset operation actives in power on and normal running mode. During system power-up, the external
reset pin must be high level input, or the system keeps in reset status. External reset sequence is as following.
External reset (only external reset pin enable):
System checks external reset pin status. If external reset pin is
not high level, the system keeps reset status and waits external reset pin released.
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.
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