This paper introduces a method for simulating PLC control using the Atmel 89S51 microcontroller, designing a controller suitable for a rigid clutch punch press. It describes the basic structure and working principle of the opto-isolated input/output circuit, focusing on the design concept of the internal keyboard display circuit, and provides the electrical schematic diagram of the punch press control. The system hardware configuration is based on the AT89S51 microcontroller. The AT89S51 is a low-power, high-performance CMOS 8-bit microcontroller with 4Kb of on-chip ISP (In-system programmable) Flash read-only memory capable of 1000 erase/write cycles. The device is manufactured using Atmel's high-density, non-volatile memory technology, compatible with the standard MCS-51 instruction set and 80C51 pinout, and includes a built-in watchdog timer (WDT) circuit. The powerful AT89S51 provides a cost-effective solution for many embedded control applications. The punch press controller designed using this microcontroller has the following features: [align=center] Figure 1 Hardware structure block diagram of the controller[/align] ● The controller adopts the PLC design concept, with high reliability and strong anti-interference capability. ● The panel features a 6-digit seven-segment LED display, which can be used to adjust parameters and display count values ​​during operation. ● Modular design, compact size, and easy installation. ● Utilizing the ISP function of the AT89S51, programs can be downloaded on-site to realize the functions of a programmable controller. Hardware Design The hardware structure of the controller is shown in Figure 1, mainly composed of a keyboard display circuit, EEPROM circuit, power-down detection, program download interface, opto-isolated input/output modules, etc. The power supply module is a switching power supply with +24V and +5V outputs designed using TOP220Y. When the system is powered off, the power-down detection circuit sends a signal to the AT89S51, and the system immediately stores the parameters and count values ​​in the EEPROM circuit. The keyboard display circuit is shown in Figure 2. To save I/O lines, the lower 3 bits of the P0 port are reused here. The working principle of this circuit is described below: During display, P3.3 and P0.0 to P0.5 are first set to high level. Then, the codes corresponding to the display content are sequentially output to the common cathode seven-segment display via a serial-in, parallel-out shift register 74HC164. The bit to be displayed is then set low, delayed for 1ms, and then set high again. As long as the frequency of this dynamic scanning is high enough (this controller uses 80Hz), the display function can be achieved due to the persistence of vision in the human eye, without flickering. When scanning the keyboard, P3.3 is set low, and the outputs of 74HC164 are all low, thus preventing interference with the display during keyboard scanning. When no key is pressed, P0.0 to P0.2 are all low. When a key is pressed, the corresponding input is read as high. Delayed debouncing determines which key was pressed, and then the corresponding key's function program is executed. The display scanning, keyboard scanning, and key debouncing of this controller are all completed within a timer interrupt. [align=center]Figure 2 Keyboard Display Circuit Structure Schematic[/align] The opto-isolated input circuit is shown in Figure 3. The input terminal and COM terminal are connected by a voltage-free contact or an NPN open-collector transistor. For reliability, the input is ON when the input current is 7mA. When the input current is less than 1.5mA, the input is OFF. The output circuit uses opto-isolated relay output to electrically isolate the internal circuit of the controller from the external circuit to prevent external interference. [align=center]Figure 3 Opto-isolated Input/Output Circuit[/align] Specific Applications The punch press control wiring is shown in Figure 4. During operation, the 6-digit digital tube on the panel displays the count value. When parameters need to be set, press the function button for 5 seconds to sequentially set parameters such as the duration of a single action, the number of times lubrication is required, and the lubrication duration. Rotate the selector switch to the single stroke position. When the slider is within the top dead center range, press the left and right buttons simultaneously. The double valve is energized, and the slider reciprocates once. When the cam rotates to the braking position, the controller de-energizes the double valve, stopping the slider at the top dead center position. [align=center]Figure 4. Punch Press Control Wiring Diagram[/align] When the selector switch is in the inching position, pressing the left and right buttons simultaneously energizes the double valve, causing the slide block to move. Releasing the buttons de-energizes the double valve, stopping the slide block. Summary The punch press controller designed using the AT89S51 microcontroller described in this paper has proven reliable and has strong anti-interference capabilities through testing. Combined with software algorithm design and photoelectric protection, it effectively prevents continuous punching and ensures operator safety. Furthermore, the AT89S51 microcontroller, with its rich instruction set, compact size, low cost, and flexible expansion capabilities, significantly improves the overall cost-effectiveness of the punch press controller.