The principle of the microcontroller reset circuit is to connect an external resistor and capacitor to the reset pin RST of the microcontroller to achieve power-on reset. The reset is valid when the reset level lasts for more than two machine cycles. The duration of the reset level must be greater than two machine cycles of the microcontroller. The specific value can be calculated by the time constant of the RC circuit.
As shown in the figure below, the microcontroller reset circuit consists of two parts: key reset and power-on reset. Among them, the STC89 series single chip is a high-level reset. Usually, a capacitor is connected to VCC on the reset pin RST, and then a resistor is connected to GND, thereby forming an RC charge and discharge loop to ensure that the microcontroller has a high level for a sufficient time on the RST pin to reset when powered on, and then returns to a low level to enter a normal working state. The typical values of this resistor and capacitor are 10K and 10uF. The key reset is to connect a switch in parallel to the reset capacitor. When the switch is pressed, the capacitor is discharged and RST is also pulled to a high level. Moreover, due to the charging of the capacitor, the high level will be maintained for a period of time to reset the microcontroller.
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Professor at Beihang University, dedicated to promoting microcontrollers and embedded systems for over 20 years.
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