The minimum system interface circuit based on AT89C52 microcontroller

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

    AT89C52 and clock circuit (including crystal oscillator, capacitor C19, C20), power-on reset circuit (including R42, C5, S3, VD1, C3, R9) constitute the minimum system of the single chip microcomputer. Among them, the crystal oscillator uses a 12MHz high-stability passive crystal oscillator, which forms an oscillator with the inverting amplifier in AT89C52, and provides a high-stability clock signal to the CPU. Capacitors C19 and C20 can play the role of frequency fine-tuning, the capacitance value is selected between 5pF~30pF, and 20pF is selected for this circuit. Capacitor C5 and resistor R42 form a power-on reset circuit. When the power supply is turned on, the power supply 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 oscillator cycles). The CPU can be reset. The function of the diode VD1 is to release the charge stored in the capacitor C5 quickly when the power is turned off, so that it can be reset reliably when the power is turned on next time. Capacitor C5 can filter out high-frequency interference and prevent the microcontroller from being reset by mistake. Button S3 and resistor R9 form a button reset circuit.