Abstract: This paper introduces a DC motor speed control system based on the S3C2410 microcontroller. Based on the introduction of the PWM speed control principle, the paper details the structural characteristics and usage of the PWM generator in the S3C2410. The core code for implementing speed control and the overall design of the speed control system are also given. Keywords: S3C2410; PWM; speed control 0 Introduction PWM (Pulse-Width Modulation) is short for pulse width modulation technology. PWM control technology, with its advantages of simple control, flexibility, and good dynamic response, has become a widely used control method in power electronics technology, and also provides a foundation for high-performance digital control of DC motors. 1 PWM Speed ​​Control Principle The conduction time of a transistor switching device is also called the conduction angle. By controlling the turn-on and turn-off time of the transistor to change the size of the conduction angle, the average voltage applied to the load can be adjusted to achieve speed control of the DC motor. This is the basic principle of PWM variable speed control technology, as shown in Figure 1. Speed ​​control is often achieved by adjusting the pulse width. Figure 1. PWM Speed ​​Control Principle 2. S3C2410 PWM Generator 2.1 Structure and Timing Principle of the PWM Generator A PWM circuit composed of discrete components generally requires the following parts: a triangular wave generation circuit, a pulse modulation circuit, and a PWM signal delay and distribution circuit. The S3C2410, as a powerful microprocessor, integrates a PWM generator containing the above three parts. With simple settings of the relevant registers, the required PWM signal can be generated. Timer/counter 0 to 3 of the S3C2410 all have PWM output functions; taking timer/counter 0 as an example, the clock signal PCLK is divided by a programmable 8-bit prescaler and clock divider, driving the logic controller within the timer. The core of the logic controller is a 16-bit down counter. We can assign different initial values ​​to the count buffer register (TCNTB0) and the compare buffer register (TCMPB0). When the timer is enabled, the data in these two registers will be loaded into the down counter (TCNT0) and the compare register (TCMP0), respectively. The design concept of the counter buffer register and compare buffer register in the S3C2410 is called "double buffering." Its advantage is that the timer can still produce a stable output when the frequency or duty cycle changes. The timing process is as follows: When the clock signal from PCLK arrives at the logic controller, the value of the down counter is automatically decremented by 1. When the value of the down counter is 0, the timer sends an interrupt request to the CPU, and one round of timing operation is completed. In auto-load mode, the initial value in the counter buffer register is automatically loaded into the down counter by hardware control for the next round of timing operation. 2.2 Principle of PWM Generator The initial value set in the compare buffer register (TCMPB0) is used to generate the PWM signal. The signal generation rule is: whenever the value of TCNT0 is equal to the value of TCMP0, the output logic level of the timer flips. The PWM pulse frequency is determined by TCNT0, while the pulse width is determined by TCMP0. The larger the value of TCMP0, the larger the duty cycle of the PWM pulse, that is, the larger the average output voltage, and vice versa. 2.3 Dead Zone Generator To control higher power devices, a dead zone generator is integrated into the PWM generator. This feature inserts a time gap between the opening of one switch and the closing of another, preventing them from being closed simultaneously. As shown in Figure 2: Figure 2 Protection Function of the Dead Zone Generator Given that TOUT0 is the PWM output pin of Timer 0, and TOUT1 is the inverted output pin of the TOUT signal, if the dead zone generator function is enabled, the output waveforms of TOUT0 and TOUT1 cannot be high simultaneously, effectively preventing output short circuits when the switches are closed simultaneously. 3. PWM Generator Program The register configuration and control process of the PWM generator are as follows: // Define dead zone width and pre-calibration value #define PRE_SCALER0 (2 << 0) #define DEAD_ZONE (20 << 16) // Macro definitions related to timing control #define START_TIMER0 (1 << 0) #define UPDATE_CFG (1 << 1) #define AUTO_RELOAD (1 << 3) #define ENABLE_DEADZONE (1 << 4) // Initial value of timing buffer 1024, motor speed control step size 2 // 1024/2 = 512 levels of speed control are possible #define MOTOR_COUNT (1024) #define MOTOR_STEP (1) // Static variable used to control speed static int nSpeed ​​=0; /* Initialize the PWM generator */ void InitPWM() { /* TOUT0 corresponds to GPB0, and TOUT1 corresponds to GPB1. Therefore, initialize GPB0/1 as the second function port. */ rGPBCON = rGPBCON & 0x3FFFF0 | 0xA; /* Dead time is 24 timing units, prescaler is set to 0, clock divider and MUX distributor take default values. */ rTCFG0 = DEAD_ZONE | PRE_SCALER0; /* Set the initial value of the counter buffer register and the comparison buffer register. */ rTCNTB0 = MOTOR_COUNT; rTCMPB0 = MOTOR_STEP * nSpeed; /* Timer 0 stops, update configuration. */ rTCON = (~ START_TIMER0) | UPDATE_CFG; /* Enable dead time generator, enter auto-reload mode, timer 0 starts. */ rTCON = NABLE_DEADZONE | AUTO_RELOAD | START_TIMER0; } Thus, PWM waveforms with dead time will be output on the TOUT0 and TOUT1 pins. The duty cycle of the PWM can be adjusted by controlling the value of the nSpeed ​​variable, thereby regulating the motor speed. 4. Overall Design of the Speed ​​Control System The system consists of an S3C2410 system board, optocouplers, a photoelectric encoder, a power drive circuit, and a DC motor, as shown in Figure 3. Figure 3: Block Diagram of the Speed ​​Control System. The S3C2410 acts as the main controller, communicating with the central control room via TCP/IP protocol, responsible for receiving control commands and reporting system status. Timer 0 of the S3C2410 serves as the PWM generator. The optocoupler is used for opto-isolation, effectively suppressing interference from the backward channel. The power drive circuit provides "H" bridge drive for the motor. The photoelectric encoder converts the sampled motor speed into a digital signal and feeds it back to the S3C2410 to achieve closed-loop control. To reduce errors, the program should perform mean filtering on the motor speed data from the photoelectric encoder. 5. Conclusion Using the S3C2410's PWM generator to control the speed of a small DC motor is a simple and easy-to-use circuit. Flexible control algorithms can be implemented in software to improve system performance. The S3C2410's powerful built-in communication and I/O functions allow for easy communication with external devices via TCP/IP, wireless RF, serial ports, etc., with LCD display, requiring only a small amount of additional circuitry. This makes control more convenient and reliable. References: [1] Li Zhining, Zhang Yingtang. Research on the application of PWM function module in PLC[J]. Microcomputer Information, 2006(25):42-45. [2] Yu Ming. ARM9 Embedded System Design and Development Tutorial[M]. Beijing: Electronic Industry Press, 2006. [3] Zhou Ligong. ARM Embedded System Experiment Tutorial[M]. Beijing: Beijing University of Aeronautics and Astronautics Press, 2004. [4] Lü Dayu, Zhu Chang'an. A scheme for PWM control using PIC[J]. Machine Tool & Hydraulics, 2004(11):133-134. [5] Jiang Changhong, Yu Wanyuan. Design of PWM speed regulation system for DC motor based on AVR microcontroller[J]. Instrumentation User, 2006,2(42).