Based on AT89C52 minimum system interface circuit

The American Atmel AT89C52 is a low-voltage, high-performance CMOS 8-bit microcontroller chip that contains 8KB of rewritable program memory and 256B of random access data memory (RAM). Atmel's high-density devices utilize non-volatile memory technology and are compatible with the standard MCS-51 instruction set. The AT89C52 features an on-chip universal eight central processor (CPU) and Flash memory cell, making it a versatile microcontroller applicable in various fields. The AT89C52 is an enhanced version of the AT89C51, which is compatible with Intel's 80C52 in terms of pinout, hardware, and operational features. The AT89C52 is available in PDIP, PQFP/TQFP, and PLCC packages to meet the requirements of different applications. To ensure proper operation of the microcontroller, a clock circuit and a reset circuit are necessary. The clock circuit includes a crystal oscillator and capacitors (C19, C20), while the power-on reset circuit consists of components such as R42, C5, S3, VD1, C3, and R9, forming the smallest single-chip system. A high-stability 12MHz crystal oscillator is used to provide a stable clock signal to the CPU, with capacitors C19 and C20 fine-tuning the frequency, typically set at 20pF. Capacitor C5 and resistor R42 create the power-on reset circuit, generating a high pulse at the CPU's reset terminal upon power-up. This high level must last longer than two machine cycles (24 oscillator periods) to effectively reset the CPU. Diode VD1 facilitates the rapid discharge of capacitor C5 when powered off, ensuring reliable reset functionality on subsequent power-ups. Additionally, capacitor C5 filters out high-frequency interference to prevent unintended resets of the microcontroller. The reset circuit is completed with key S3 and resistor R9.

The AT89C52 microcontroller is designed for flexibility and efficiency in embedded systems. The architecture supports a range of applications, from simple control systems to complex automation tasks. The 8KB of program memory allows for substantial code storage, while the 256B of RAM provides adequate space for variable storage during program execution.

The clock circuit, which utilizes a 12MHz crystal oscillator, is crucial for maintaining synchronization within the microcontroller. The choice of a high-stability oscillator ensures that the CPU operates reliably under varying conditions. The capacitors C19 and C20 serve to stabilize the frequency output, which is critical for applications requiring precise timing.

The reset circuit is equally important, as it guarantees that the microcontroller starts in a known state. The combination of capacitor C5 and resistor R42 ensures that the reset signal is generated reliably upon power-up. The inclusion of diode VD1 is a thoughtful design choice, as it enhances the reset circuit's performance by allowing for quick discharge of the capacitor, thus preparing the microcontroller for the next operational cycle without delays.

In summary, the AT89C52 microcontroller is a robust and versatile component suitable for a wide range of applications, featuring essential circuits for clock generation and reset functionality that ensure reliable operation in embedded systems.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.