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What issues should be considered in application system hardware design? [Copy link]

(1) Memory expansion: Capacity requirements. When selecting, the internal memory resources of the microcontroller should be considered. If the requirements can be met, there is no need to expand. When expansion is necessary, pay attention to the type, capacity and interface of the memory. Generally, try to leave room and reduce the number of chips as much as possible. Choose the appropriate method, ROM and RAM form, whether RAM needs power-off protection, etc. (2) I/O interface expansion: When expanding the I/O interface of the microcontroller application system, the volume, price, load capacity, function and other aspects should be considered. The appropriate address decoding method should be selected according to the number of external expansion circuits and the internal resources of the selected microcontroller (the number of free address lines). (3) Input channel design: Input channel design includes the design of switch quantity and analog input channel. For switch quantity, the interface form, voltage level, isolation method, expansion interface, etc. should be considered. The design of analog channels should be combined with the signal detection link (sensor, signal processing circuit, etc.). It should be selected according to the system's requirements for speed, accuracy and price. At the same time, it needs to match the performance of sensors and other equipment. It is necessary to consider the sensor type, the form of the transmitted signal (current or voltage), linearization, compensation, photoelectric isolation, signal processing method, etc. It is also necessary to consider the selection of A/D converters (conversion accuracy, conversion speed, structure, power consumption, etc.) and related circuits, expansion interfaces, and sometimes software design. High-precision analog-to-digital converters are very expensive, so the requirements for A/D converters should be reduced as much as possible, and functions that can be implemented by software should be implemented by software as much as possible. (4) Output channel design: Output channel design includes the design of switch quantity and analog output channels. Switch quantity should consider power and control method (relay, thyristor, triode, etc.). Analog output should consider the selection of D/A converters (conversion accuracy, conversion speed, structure, power consumption, etc.), the form of output signals (current or voltage), isolation method, expansion interface, etc. (5) Design of human-machine interface: The design of human-machine interface includes input keyboard, switch, dial, start/stop operation, reset, display, printing, indication, alarm, etc. The input keyboard, switch, dial should consider the type, number, parameters and related processing (such as key debounce processing). The start/stop and reset operations should consider the mode (automatic, manual) and its switching. The display should consider the type (LED, LCD), the type of displayed information, multiples, etc. In addition, the expansion interface of various human-machine interfaces should be considered. (6) Design of communication circuit: The microcontroller application system is often used as a field measurement and control equipment, and often forms a measurement and control network with the host computer or the same position machine. It needs to have data communication capabilities, and is usually designed to RS-232C, RS-485, infrared transceiver and other communication standards. (7) Design and production of printed circuit boards: The design of circuit schematics and printed circuit boards is often designed using professional design software, such as Protel, OrCAD, etc. Designing a printed circuit board requires a lot of skills and experience. After designing the printed circuit board diagram, it should be sent to a professional manufacturer for production. After installing the components on the produced printed circuit board, the production is completed. (8) Consideration of load tolerance: The load capacity of the microcontroller bus is limited. For example, the load capacity of the P0 port of the MCS-51 is 4mA, which can drive up to 8 TTL circuits. The load capacity of the P1~P3 ports is 2mA, which can drive up to 4 TTL circuits. If there are many external loads, the bus drive method should be adopted to improve the load tolerance of the system. Commonly used drivers include: unidirectional driver 74LS244, bidirectional driver 74LS245, etc. (9) Consideration of signal logic level compatibility: In the designed circuit, there may be both TTL and CMOS devices, and there are also non-standard signal levels. The corresponding level compatibility and conversion circuits should be designed. When there are RS-232 and RS-485 interfaces, level compatibility and conversion must be achieved. Commonly used integrated circuits include MAX232, MAX485, etc. (10) Configuration of the power supply system: The microcontroller application system must have a power supply. The number of power supply groups, output power, and anti-interference should be considered. You should be familiar with the application of commonly used three-terminal regulators (78хх series, 79хх series) and precision power supplies (AD580, MC1403, CJ313/336/385, W431). (11) Implementation of anti-interference: Taking necessary anti-interference measures is an important part of ensuring the normal operation of the microcontroller system. It includes chip and device selection, decoupling filtering, printed circuit board wiring, channel isolation, etc.
This post is from Microcontroller MCU
 

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