说明：  一个单片机应用系统的硬件电路设计包含两部分内容：一是系统扩展，即单片机内部的功能单元，如ROM、RAM、I/O、定时器/计数器、中断系统等不能满足应用系统的要求时，必须在片外进行扩展，选择适当的芯片，设计相应的电路。二是系统的配置，即按照系统功能要求配置外围设备，如键盘、显示器、打印机、A/D、D/A转换器等，要设计合适的接口电路。
(Application of a single-chip hardware circuit design contains two parts: First, expanding the system, that is, single-chip s internal functional unit, such as ROM, RAM, I/O, timer/counter, interrupt system can not meet the application system the request must be expanded in the chip, select the appropriate chips, the design of the corresponding circuit. Second, the system configuration, that is the functional requirements in accordance with the system configuration peripherals such as keyboards, monitors, printers, A/D, D/A converters and so on, to design an appropriate interface circuit.)