Three C51 microcontroller power-on reset delay circuit diagrams

The following delayed reset circuits are all formed by using the charging time of an external RC branch connected to the RST pin of the microcontroller. A typical reset circuit is shown in Figure (a), where the resistor and capacitor values ​​are provided in the original manual. Figure (b) is a simplified reset circuit. Figure (c) adds a diode D on the basis of figure (a), which helps to quickly discharge the capacitor C and prepare for the next power-on reset delay. After experiencing a series of delays, the microcontroller begins to enter the normal program running state according to the operating frequency of the clock source.