Minimum system interface circuit based on AT89C52 microcontroller

　　AT89C52 is a low-voltage, high-performance CMOS 8-bit microcontroller produced by Atmel Company in the United States. It contains 8KB of rewritable program memory and 256B of random access data memory (RAM). The device adopts Atmel's high-density, non-volatile memory. Produced with volatile storage technology, it is compatible with the standard MCS-51 instruction system. It is equipped with a general-purpose 8-bit central processing unit (CPU) and Flash storage unit on-chip. The powerful AT89C52 microcontroller can be flexibly used in various control fields. The AT89C52 microcontroller is an enhanced version of the AT89C51 microcontroller and is compatible with Intel's 80C52 in terms of pin arrangement, hardware composition, operating characteristics and command system. AT89C52 has three packaging forms: PDIP, PQFP/TQFP and PLCC to meet the needs of different products. When the microcontroller operates normally, it requires a clock circuit and a reset circuit. The microcontroller reset and crystal oscillator circuit are shown in the figure.

　　AT89C52, clock circuit (including crystal oscillator, capacitor C19, C20), and power-on reset circuit (including R42, C5, S3, VD1, C3, R9) constitute the minimum system of the microcontroller. Among them, the crystal oscillator uses a 12MHz highly stable passive crystal oscillator, which forms an oscillator with the reverse amplifier in the AT89C52 to provide a highly stable clock signal to the CPU. Capacitors C19 and C20 can play a role in frequency fine-tuning. The capacitance value can be selected between 5pF and 30pF. For this circuit, 20pF is selected. Capacitor C5 and resistor R42 constitute a power-on reset circuit. When the power is turned on, the power charges the capacitor C5 and generates a high pulse at the reset terminal of the CPU. As long as the high level is maintained for longer than two machine cycles (24 oscillation cycles). The CPU can be reset. The function of the diode VD1 is to quickly release the charge stored in the capacitor C5 when the power is turned off, so that it can be reliably reset the next time the power is turned on. Capacitor C5 can filter out high-frequency interference and prevent the microcontroller from erroneously resetting. Button S3 and resistor R9 constitute a button reset circuit.