Design principles that should be followed in the expansion and configuration of single-chip hardware systems

　　The hardware circuit design of a single-chip microcomputer application system includes two parts: one is system expansion, that is, when the functional units inside the single-chip microcomputer, such as ROM, RAM, I/O, timer/counter, interrupt system, etc., cannot meet the requirements of the application system, they must be expanded outside the chip, and appropriate chips must be selected and corresponding circuits designed. The second is system configuration, that is, peripheral devices such as keyboards, monitors, printers, A/D, D/A converters, etc. must be configured according to the system functional requirements, and appropriate interface circuits must be designed.

　　The expansion and configuration of the system should follow the following principles:

　　1. Choose typical circuits as much as possible and conform to the conventional usage of single-chip microcomputers to lay a good foundation for the standardization and modularization of hardware systems.

　　2. The configuration level of system expansion and peripheral equipment should fully meet the functional requirements of the application system and leave appropriate room for secondary development.

　　3. The hardware structure should be considered together with the application software solution. The hardware structure and software solution will have mutual influence. The principle of consideration is: the functions that can be realized by software should be realized by software as much as possible to simplify the hardware structure. However, it must be noted that the hardware functions realized by software generally have a longer response time than hardware implementation and occupy CPU time.

　　4. The performance of related devices in the system should be matched as much as possible. For example, when a CMOS chip single chip is used to form a low-power system, all chips in the system should be low-power products as much as possible.

　　5. Reliability and anti-interference design are an indispensable part of hardware design, which includes chip, device selection, decoupling filtering, printed circuit board wiring, channel isolation, etc.

　　6. When there are many peripheral circuits of the microcontroller, its driving capability must be considered. When the driving capability is insufficient, the system will not work reliably. The bus load can be reduced by adding line drivers to enhance the driving capability or reducing the chip power consumption.

　　7. Try to design the hardware system in the direction of "single chip". The more system components there are, the stronger the mutual interference between the components, the greater the power consumption, and the inevitable reduction of system stability. As the functions integrated in the microcontroller become more and more powerful, a true system-on-chip SoC can be realized. For example, the μPSD32×× series products recently launched by ST integrate an 80C32 core, a large-capacity FLASH memory, SRAM, A/D, I/O, two serial ports, a watchdog, a power-on reset circuit, etc. on a single chip.