Abstract: This paper introduces the hardware and software structure of a stepper motor control system based on TMS320LF2407. The event management module of a DSP is used to generate PWM waveforms for stepper motor control. The design is simple, practical, and highly scalable. Keywords: Digital Signal Processor, Stepper Motor, Event Management Module Introduction DSP ( Digital Signal Processor) is a microprocessor particularly suitable for digital signal processing. It adopts an advanced hardware and software structure, separating its program and data spaces, allowing simultaneous access to instructions and data. It also features event module management and fast interrupt handling. With its high performance and increasingly lower cost, it is increasingly widely used in information processing and control systems. The TMS320LF2407 chip, as a fixed-point DSP controller, is particularly suitable for control systems. Its included event management module can easily realize digital motor control. Stepper motors are a common actuator in digital control systems, receiving digital control signals (electrical pulse signals) and converting them into corresponding angular or linear displacements. Stepper motors have the advantage of open-loop control with no cumulative error, and the control system structure is simple, thus leading to their widespread application. This article introduces the design of a stepper motor control system based on the TMS320LF2407. 1 System Hardware Composition The entire system consists of five parts: the TMS320LF2407 DSP central controller, the stepper motor and driver, the photoelectric encoder, the keyboard and LCD display, and the peripheral power supply circuit and watchdog reset circuit, as shown in Figure 1. In this system design, the given speed (position) is set via the keyboard, and the stepper motor's speed (position) is controlled by a central controller TMS320LF2407 that generates PWM pulse signals. Closed-loop control can be achieved by sampling and detecting the stepper motor's speed (position) using an optical encoder, or open-loop control can be used without a speed (position) signal. Multiple variables and parameters in the above process can be intuitively displayed on the LCD screen. The entire hardware structure is simple and intuitive, and the central controller TMS320LF2407 has abundant I/O and interrupt resources, providing room for expansion based on this design. [align=center] Figure 1 Hardware Principle Block Diagram[/align] This design uses a 55BF03 three-phase reactive stepper motor, which receives digital control signals (electrical pulse signals) and converts them into corresponding angular or linear displacements. This design uses a PWM ring pulse signal generated by a TMS320LF2407 central controller, which is then signal-distributed and amplified to transmit to the stepper motor to control its angular position or linear displacement. Therefore, the stepper motor drive structure consists of the following parts: pulse signal, signal distribution, power amplification, stepper motor, and load, as shown in Figure 2. Based on considerations of torque, smoothness, noise, and reduced angle, this design generates a three-phase, six-step signal to control the stepper motor. The power-on sequence is A-AB-B-BC-C-CA, the step angle is 1.5°, and the power amplification uses a typical single-voltage drive method. [align=center]Figure 2 Stepper Motor Drive Block Diagram[/align] For the photoelectric encoder, an incremental encoder or an absolute encoder can be selected. The former is suitable for speed detection, and the latter for position detection. The A and B signals of the encoder are connected to the corresponding pins of the quadrature decoding pulse unit QEP, which can detect the speed (position) of the stepper motor and determine its rotation direction. In terms of display, liquid crystal displays (LCDs), whether dot-matrix or graphic, can display not only characters and numbers, but also various graphics, curves, and Chinese characters. They also offer features such as scrolling, animation, flashing, and text display, and boast numerous advantages unmatched by other displays, including low power consumption, small size, light weight, and ultra-thin design, making them extremely versatile. This system design utilizes the HY-12864 graphic LCD, which incorporates two HD61202 LCD control drivers. The maximum display area of ​​this screen is 128*64. The following control signals from the HY-12864—read/write signal (R/W), data or command signal (RS), left and right screen chip select signals (CS1, CS2), enable signal (E), and data bus (DB0-DB7)—are directly controlled by the I/O ports of the TMS320LF2407. The connection schematic is shown in Figure 3 below. [align=center]Figure 3 Hardware connection diagram of LCD display HY-12864 and TMS320LF2407[/align] 2 Software Design The entire software design includes the main program, stepper motor driver, LCD display driver, key scan interrupt program, encoder detection and conversion program, etc. The stepper motor driver and encoder detection and conversion program are described in detail below. The stepper motor driver design fully utilizes the event management module of the TMS320LF2407 controller. Each TMS320LF2407 has a 16-bit comparator register CMPRx (x=4, 5, 6). Each comparator has two PWM output pins, generating three PWM output signals to control the motor speed (position). The polarity of the output pins is determined by the control bits of the control register (ACTR), selecting either a high or low level as the enable signal as needed. In PWM signal modulation, a carrier wave with a certain period is required. Timer 3 is used in this process. It takes the internal CPU clock as input and operates in continuous increment/decrement counting mode to generate PWM pulse output. The generated pulse is a circular variable pulse. An interrupt is generated when the T3PR timing period underflows or overflows, refreshing the period value and adjusting the PWM. The calculation method is as follows: The relationship between motor speed and electrical pulse frequency f: Finally, in this design, the given speed is converted into the corresponding binary code. Dividing 29297 by the given speed gives the PWM base. The resulting PWM value is then multiplied by 3 to obtain the period value of Timer 3's T3PR, corresponding to PWM pulse outputs at different frequencies, as shown in Figure 4, the motor operation interrupt program flowchart. [align=center] Figure 4 Motor operation interrupt program flowchart[/align] The photoelectric encoder detection utilizes the quadrature decoding pulse unit QEP. A and B are connected to the two channels QEP1 and QEP2 of the quadrature decoding pulse unit, respectively. The quadrature decoding pulse unit (QEP) has a direction detection function. Its direction detection logic identifies which of the two sequences is the leading sequence, and then generates a direction signal as the direction input for the selected timer. If the leading sequence is input to QEP1, the selected timer increments; otherwise, if the leading sequence is input to QEP2, the selected timer decrements. Note that both edges of the two quadrature input pulses are counted by the quadrature decoding pulse unit, thus generating a clock frequency four times that of each input sequence. In this system, timer 2 is used as a counter. It takes the clock generated by the quadrature decoding pulse unit as its input and works together with the quadrature decoding pulse units QEP1 and 2 to detect the encoder signal and convert it into the corresponding speed (position) signal. The stepper motor control scheme introduced in this paper is innovative in that it utilizes the event management module of the TMS320LF2407 to simply and effectively control the speed (position) of the stepper motor. The system also includes a corresponding human-machine interface for displaying and operating relevant variables, and the system has sufficient resources for easy expansion. References [1] Liu Heping. TMS320LF240X DSP Structure Principle and Application. 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