Based on AT89C52 minimum system interface circuit
Posted on Mar 28, 2007 10363
American Atmel AT89C52 is produced by low-voltage, high-performance CMOS 8-bit microcontroller chip contains 8KB of rewritable program memory and 256B of random access data mem
ory (RAM), Atmels high-density devices, non volatile memory technology production, compatible with the standard MCS-51 instruction set, on-chip configuration universal eight central processor (CPU) and Flash memory cell, powerful AT89C52 microcontroller control can be flexibly applied to various fields. AT89C52 single-chip microcontroller AT89C51 belongs enhanced with Intels 80C52 in pinout, hardware, features and aspects of the work instruction compatible systems. AT89C52 has PDIP, PQFP/TQFP and PLCC and other three packages to suit the needs of the microcontroller when different products work properly, we need to have a clock circuit and a reset circuit. Reset the microcontroller, crystal oscillator circuit as shown in FIG. AT89C52 clock circuit (including the crystal oscillator, capacitors C19, C20), power-on reset circuit (including R42, C5, S3, VD1, C3, R9) constitute the smallest single-chip system. Among them, the selection of high-stability crystal oscillator passive 12MHz crystal oscillator, which is the reverse with AT89C52 oscillator amplifiers provide high stable clock signal to the CPU. Capacitors C19, C20 can play a role in fine-tuning the frequency, capacitance values between 5pF ~ 30pF selection, the circuit election 20pF. Capacitor C5 and resistor R42 constitute a power-on reset circuit. When the power is turned on, the power supply to charge the capacitor C5, the reset terminal of the CPU generates a high pulse. Just to maintain the high level longer than two machine cycles (24 oscillator periods). CPU can be reset. Diodes VD1 role when powered off the capacitor C5 allows rapid release of the stored charge, so that the next reliable reset on power. Capacitor C5 can filter out high frequency interference, to prevent misuse microcontroller reset. Key S3 and resistor R9 constitute key reset circuit.