SN32F760 Series
32-Bit Cortex-M0 Micro-Controller
SONiX TECHNOLOGY CO., LTD
Page 46
Version 2.0
voltage and MCU operates normally. When VDD is below “0.7V x (R1 + R2) / R1”, the C terminal of the PNP transistor
outputs low voltage and MCU is in reset mode.
Decide the reset detect voltage by R1, R2 resistances. Select the right R1, R2 value to conform the application. In the
circuit diagram condition, the MCU’s reset pin level varies with VDD voltage variation, and the differential voltage is
0.7V. If the VDD drops and the voltage lower than reset pin detect level, the system would be reset. If want to make the
reset active earlier, set the R2 > R1 and the cap between VDD and C terminal voltage is larger than 0.7V. The external
reset circuit is with a stable current through R1 and R2. For power consumption issue application, e.g. DC power
system, the current must be considered to whole system power consumption.
Note: Under unstable power condition as
brown out reset, “Zener diode reset circuit” and “Voltage bias
reset circuit” can protects system no any error occurrence as power dropping. When power drops
below the reset detect voltage, the system reset would be triggered, and then system executes
reset sequence. That makes sure the system work well under unstable power situation.
3.1.4.5
EXTERNAL RESET IC
MCU
VDD
VSS
VCC
GND
RST
Reset
IC
VDD
VSS
RST
Bypass
Capacitor
0.1uF
The external reset circuit also uses external reset IC to enhance MCU reset performance. This is a high cost and good
effect solution. By different application and system requirement to select suitable reset IC. The reset circuit can improve
all power variation.
3.1.5
SOFTWARE RESET
The entire MCU, including the core, can be reset by software by setting the SYSRESREQ bit in the
register in Cortex-M0 spec.
The software-initiated system reset sequence is as follows:
1.
A software reset is initiated by setting the SYSRESREQ bit.
2.
An internal reset is asserted.
3.
The internal reset is deasserted and the MCU loads from memory the initial stack pointer, the initial program
counter, and the first instruction designated by the program counter, and then begins execution.
