Microcontroller hardware system design principles [PCB design]
Update date：2012-6-27
A hardware circuit design for microcomputer application system consists of two parts:
First, the system expansion, the MCU internal functional units, such as ROM, RAM, I / O, timer / counter, interrupt system and so can not meet the requirements of the application system must be in the off-chip extension, select the appropriate chip design the corresponding circuit.
Second, the configuration of the system configuration in accordance with the system functional requirements of peripheral devices such as keyboards, monitors, printers, the A / D and the D / A conversion, etc., to design a suitable interface circuit.
Extension and configuration of the system should follow the following principles:
(1) If possible, choose a typical circuit, and in accordance with the SCM common usage, to lay a good foundation for the standardization of hardware systems, modular.
(2) system expansion and peripheral equipment configuration levels should fully meet the functional requirements of the application system. And leave appropriate room for the second express.
(3) hardware architecture should be combined with application software programs to be considered. Hardware architecture and software programs will have a mutual influence, consider the principle is: the software to achieve the functionality as much as possible by the software to simplify the hardware structure. It must be noted, by the software to the hardware features, the general response time than the hardware to achieve long, and the CPU time.
(4) in the device as possible the performance to match. Such as selection of the CMOS chip microcontroller constitute a low-power system, all the chips in the system should, where possible choose low-power products.
(5) reliability and anti-jamming design is an essential part of the hardware design, which includes the chip, device selection, decoupling filtering, the printed circuit board layout, the channel isolation.
(6) single-chip peripheral circuits more, we must consider its drive capability. Drive capability is insufficient, the system is not working, reliable, and can enhance the driving capability by an additional line driver reduces chip power consumption to reduce the bus load.
(7) as far as possible the direction of the "monolithic" design hardware systems. More system components, devices interfere with each other, the stronger the power consumption increases, inevitably reduce the small stability of the system n integrated functionality with the microcontroller chip is growing, the real system on a chip SoC can be achieved, such as ST company recently introduced PSD32XX series on a single chip integrated plant Ror32 nuclear, the 9H memory of large capacity n, of sRAM, the A / D, I / O and two serial ports, watchdog timer, power-on reset circuit and so on.
General microcontroller will have some flags register can be used to determine the summer bits reason; Also can do some of the signs in RAM. Reset every time the program by the judgment of these signs, you can determine the reset reason; can also jump directly to the appropriate program according to the different signs. So they can program runs continuous, the user will not be used to detect to the program is reset.
Set up a number of registers in the timer interrupt which accumulate, and then added to the pre-set value (a long time), the SET flag, these actions are in the interrupt program inside. The main program only need to check the flag. But pay attention to the flag to use later, remember to clear, there have to remember to clear in the use of the interrupt inside the base accumulator.
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