Overall Plan The software's main tasks have been outlined in the overall design. When moving to the detailed software design, it is essential to integrate the hardware structure to further clarify the specific responsibilities of the software, determine the implementation methods, and allocate resources efficiently. 1. Programming Technology A well-structured software system is fundamental for building a high-performance microcontroller application. In program design, adopting a structured programming approach helps break down functions into modular components. There are generally two common design strategies: a. Modular Programming Modular programming involves dividing a large program into smaller, independent modules, each handling a specific function. Each module can be designed, coded, and tested separately before being combined into the final system. This method simplifies debugging and allows reuse across different programs. However, managing the interconnections between modules can sometimes be challenging. b. Top-down Programming Top-down programming starts with the main program and gradually breaks it down into subroutines or functions. Initially, placeholders are used for these subprograms, and once the main logic is set, each part is compiled and integrated. This approach aligns with human thinking patterns, making it easier to identify errors early. However, any error at the higher level can affect the entire system, requiring extensive revisions when changes are made. 2. Software Development Once the software structure and programming techniques are decided, the next step is to actually write the code that translates the design into functional software. a. Establishing a Mathematical Model To implement the system, it is necessary to define the mathematical relationships between input and output variables. This model serves as the foundation for accurate system performance and varies depending on the task requirements. b. Drawing a Program Flowchart Creating a flowchart before writing the code improves the efficiency of the software development process. It provides a visual representation of the program’s logic, making it easier to translate into actual code. Beginners especially benefit from this method, as it offers a clear path to follow during development. c. Writing the Code After completing the flowchart, the actual coding begins. Assembly language is commonly used for microcontroller programming due to its direct control over hardware, offering speed but limited readability. For complex data operations, higher-level languages like C (e.g., C51) or PL/M may be more suitable. Careful attention must be given to resource allocation, subroutine parameters, and data structures to meet system accuracy and reliability requirements. In terms of memory allocation, frequently used data buffers should be placed in internal RAM. Flags should be stored in the bit-addressable area (20H–2FH). The user stack area must be defined with sufficient size, while the remaining space can act as a data buffer. During the coding process, symbolic instructions are used based on the flowchart to generate the assembly source code. It should follow the standard syntax of the MCS-51 assembly language. While fulfilling the system's functions, the design must also ensure reliability through features like digital filtering, software traps, and protection mechanisms. Adding comments where necessary enhances the readability of the program. 3. Program Design After developing and testing individual program modules, they are assembled or compiled and connected according to the software architecture. This step ensures the integration of all parts into a complete system. Paying attention to software interfaces during this phase is crucial for smooth operation. What Should Be Considered in the Hardware Design of a Microcontroller System? (1) Memory Expansion: When choosing a microcontroller, consider its internal memory capacity. If it meets the needs, no expansion is required. If expansion is necessary, pay attention to the type, capacity, and interface of the memory. Leave some room for future growth and minimize the number of chips used. Choose appropriate ROM/RAM configurations and ensure power-down protection for RAM. (2) I/O Interface Expansion: When expanding I/O interfaces, consider factors such as volume, cost, load capacity, and functionality. Select an appropriate address decoding method based on the number of external circuits and available address lines in the microcontroller. (3) Input Channel Design: Input channels include both digital and analog signals. For digital inputs, consider interface types, voltage levels, isolation methods, and expansion options. Analog channels require matching with sensors, signal processing circuits, and A/D converters. Consider conversion accuracy, speed, and cost, as well as signal conditioning and isolation. (4) Output Channel Design: Output channels involve both digital and analog outputs. Digital outputs should consider power and control methods, while analog outputs need D/A converters, signal forms, isolation, and expansion interfaces. (5) Human-Machine Interface Design: This includes keyboards, switches, displays, alarms, and more. Consider button debounce, display types, and interface expansion for better usability. (6) Communication Circuit Design: Common communication standards include RS-232C, RS-485, and infrared. These allow the microcontroller to interact with other devices in a network. (7) PCB Design and Manufacturing: Use professional tools like Protel or OrCAD to create schematics and PCB layouts. After designing, send the layout to a manufacturer for production. (8) Load Tolerance: The MCU bus has limited driving capability. For example, the P0 port of the MCS-51 can drive up to 8 TTL circuits. If more loads are needed, use drivers like 74LS244 or 74LS245 to increase capacity. (9) Signal Level Compatibility: Ensure compatibility between TTL and CMOS devices, and between different signal levels. Use level converters like MAX232 or MAX485 for interfaces like RS-232 or RS-485. (10) Power Supply Configuration: The system requires stable power. Consider the number of power supplies, output power, and noise immunity. Familiarize yourself with common regulators like 78xx, 79xx, and precision power supplies. (11) Anti-Interference Measures: Implement shielding, decoupling, proper PCB routing, and isolation techniques to reduce interference and ensure reliable system operation.
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