Microcontroller power-on reset circuit

Integral power-on reset

Commonly used power-on or switch reset circuits are shown in the figure. After powering on, RST remains high for a period of time due to the charging of capacitor C3 and the action of the inverting gate. When the microcontroller is already running, pressing the reset button K and then releasing it can also make RST high level for a period of time, thereby realizing the power-on or switch reset operation.

Based on actual operating experience, the reference values ​​of capacitance and resistance of this reset circuit are given below.

In Figure 3: C: =1uF, Rl=lk, R2=10k

Dedicated chip reset circuit

The function of the power-on reset circuit in the control system is to start the microcontroller to start working. However, when the power supply is powered on and the voltage is abnormal or interferes with normal operation, the power supply will have some unstable factors, which may have a serious impact on the stability of the microcontroller. Therefore, when the power supply is powered on, the delayed output outputs a reset signal to the chip. Another function of the upper reset circuit is to ensure the power supply voltage during normal operation. If there is an abnormality in the power supply, a forced reset will be performed. The reset output pin outputs a low level for three (12/fc s) or more instruction cycles, and the reset program begins to initialize the initial state inside the chip. Waiting to receive input signals (such as remote control signals, etc.).

Analysis of power-on reset circuit principle

The 5V power supply is input through pin 2 of MC34064, and pin 1 can output a rising edge to trigger the reset pin of the chip. Electrolytic capacitor C13 adjusts the reset delay time. When the power is turned off, the residual charge on the electrolytic capacitor C13 forms a loop through D13 and the internal circuit of MC34064, and the charge is released. To prepare for the next reset to be enabled.