I. Introduction With the development of microelectronics and computer technology, programmable logic controllers (PLCs) have made rapid progress. Their functions have far exceeded the scope of logic control and sequential control. Effectively integrated with computers, they can perform analog control and have remote communication capabilities. Some consider them one of the three pillars of modern industrial control (i.e., PLC, robots, and CAD/CAM). Currently, programmable logic controllers (PLCs) are widely used in metallurgy, mining, machinery, and light industry, providing a powerful tool for industrial automation. II. Basic Structure of a PLC PLCs adopt a typical computer architecture, mainly including a CPU, RAM, ROM, and input/output interface circuits. If we consider a PLC as a system, this system consists of input variables, PLC, and output variables. Various external switch signals, analog signals, and sensor-detected signals all serve as input variables for the PLC. These are input to the PLC's internal registers via external terminals, and after internal logic operations or other processing, they are sent to the output terminals. These are the PLC's output variables, which are used to control peripheral devices. III. Control Methods and Research 1. Introduction to the Special Functions of FP1 (1) Pulse Output The output terminal Y7 of FP1 can output pulses. The pulse frequency can be adjusted by software programming. Its output frequency range is 360Hz～5kHz. (2) High-Speed ​​Counter (HSC) FP1 has a high-speed counter inside, which can simultaneously input two pulses. The maximum counting frequency is 10kHz, and the counting range is -8388608～+8388607. (3) Input Delay Filter The input terminal of FP1 adopts input delay filtering, which can prevent unreliability caused by mechanical jitter of the switch. Its delay time can be adjusted as needed. The adjustment range is 1ms～128ms. (4) Interrupt Function There are two types of interrupts for FP1. One is external hard interrupt and the other is internal timer interrupt. 2. Speed ​​Control of Stepper Motor FP1 has an SPD0 instruction. This instruction, together with the pulse output function of HSC and Y7, can realize speed and position control. The speed control ladder diagram is shown in Figure 1, the control mode parameters are shown in Figure 2, and the pulse output frequency setting curve is shown in Figure 3. 3. The control system program runs as follows: The pulse output by Y7 serves as the clock pulse for the stepper motor, which generates a beat pulse through the driver to control the stepper motor's operation. Simultaneously, Y7 is connected to the PLC's input contact X0, and the pulses are sent to the PLC's internal HSC via X0. The HSC counts the number of pulses from Y7, and when a predetermined value is reached, an interrupt occurs, causing the pulse frequency of Y7 to switch to the next parameter, thus achieving more accurate position control. The ladder diagram for this control is shown in Figure 4. [align=center] Figure 4 Control Ladder Diagram[/align] The control system's operating program: The first line clears DT9044 and DT9045, preparing for HSC counting; the second to fifth lines establish the parameter table, with parameters stored in the data register area starting at address DT20; the last line initiates the SPD0 instruction, which, when executed, retrieves the set parameters starting from DT20 and completes the corresponding control requirements. From the first line, we know that the first parameter is K0, a characteristic value of the PULSE mode, thus defining the output mode. The second parameter is K70, corresponding to a pulse frequency of 500Hz, so Y7 emits pulses at a frequency of 500Hz. The third parameter is K1000, meaning that after 1000 pulses at this frequency, it switches to the next frequency. The next frequency, which is the last parameter, is K0, so when this step is executed, the pulses stop, and the motor stops. Therefore, when this program is run, the stepper motor can drive the controlled object at a specified speed and a predetermined number of revolutions, causing it to reach a predetermined position and then automatically stop. III. Conclusion Programmable logic controllers (PLCs) can conveniently control the speed and position of motors, enabling convenient and reliable operation of various stepper motors and completing various complex tasks. It represents an advanced industrial automation revolution and accelerates the realization of mechatronics.