Embedded system is the combination of advanced computer technology, semiconductor technology, electronic technology and specific applications in various industries. It is a system in which hardware and software are closely tied together. This feature determines that it must be a technology. Intensive, highly fragmented, and constantly innovative knowledge integration system. Most of the current embedded system talents are cultivated in the workplace. Domestic colleges and universities still rarely set up an undergraduate program of embedded systems, just to meet the needs of the society, and to open relevant courses and study for some professional students. Embedded system design is a very practical course, and its theory is still developing. Without a good practice platform, embedded system technology is difficult to master, and students' skills are not improved. Students cannot adapt to the needs of the market.
Some existing embedded system experimental platforms are very mature, and the products cover all major company chips from ARM7 to ARM9. These platforms are not only realize the full function of the ARM chip, but also extend the related functions on the experimental board, providing almost all interfaces on the experiment board, so that students can fully access the programming of the type interface, which is very good. Experiment and develop various software on the experimental board. However, such platforms also have considerable deficiencies. On the experimental platform provided by the students, students can only complete the practice of the software part, but the analysis and design of the hardware part can not get a good exercise. ARM development is a combination of hardware and software. In terms of ARM hardware design, students still have considerable deficiencies. The educational resources in this area are currently scarce. A suitable ARM experimental platform is needed to comprehensively improve students' softness. Hardware level. This design provides some suggestions for the construction of the ARM experimental platform.
2 Hardware implementation of LPC2368 embedded experimental platformIn order to allow students to fully access the hardware design of the ARM board and better achieve the teaching purpose, the experimental platform uses the core board and the expansion board hardware to separate the design (as shown in Figure 1). Only one ARM minimum system is designed on the core board, and the port is pulled out for expansion, and the relevant interface is expanded on the expansion board as needed. This kind of simplification makes students not only able to have a deep understanding of the simple ARM minimum system, but also can design the peripheral expansion circuit, and finally the programming, software and hardware capabilities are improved at the same time, deepen learning. Impressions and interests.
According to the design of the program, considering the teaching requirements, cost issues and ease of development, the system uses the 32-bit processor LPC2368 based on the ARM7TDMI processor core from NXP (formerly PHILIPS Semiconductor). It embeds up to 512KB of ISP/IAP Flash and up to 58KB of SRAM, which can run uclinux and uc/OS-II without expanding storage and memory, simplifying design and reducing costs while meeting the requirements of the experimental platform. At the same time, LPC2368 also supports 10/100 Ethernet, full-speed (12Mbps) USB 2.0 and CAN 2.0B, multiple serial communication interfaces (3 II C, 1 IIS, 4 UART and 3 SPI/SSP) enhanced design. Flexibility, greater buffering and higher processing power; 10-bit A/D and D/A converters and an IRC oscillator with SD memory card interface to choose from. Powerful and rich in interfaces, it is ideal for building experimental platforms.
2.1 Core board design
In order for an embedded processor to work, it must have a power supply, a clock signal must be added, and a reset signal must be provided. If the chip does not have on-chip memory or the internal memory is not large enough, then the memory system needs to be added before the embedded processor chip can work properly. These circuits, which provide the conditions necessary for the operation of the embedded processor, together with the chip constitute the smallest system. All the I/O interfaces of the LPC2368 are taken out from the core board to facilitate hardware expansion and interface design on the motherboard. Therefore, the core board part of this design includes the ARM chip, power supply, clock, reset, and I/O outlet.
2.2 expansion board design
The expansion board in the experimental platform, mainly through the students to design the relevant peripheral interface hardware to improve the students' hardware hands-on ability. The I/O port of the motherboard is led out through the slot, which is convenient for extending the peripheral hardware interface required for the experiment design. The LPC2368 is powerful and has a rich interface. It has multiple serial communication interfaces, USB devices, network interfaces and SD card interfaces.
This design only completes part of the hardware unit circuit. Students can design the hardware circuit of each interface part according to the actual situation, then draw the PCB and make the plate, and repeat the test to success. This can improve the students' practical ability, prevent the paper on the soldiers, the hardware circuit design process, and the specific design details to get a good opportunity for refining. Then you can connect your own peripheral interface to the I/O port, port the operating system to the motherboard, and learn to write drivers to drive external circuits. Hardware design and software programming are consolidated and improved at the same time.
2.2.1 UART serial port design
The LPC2368 has four serial interfaces. In addition to standard data transmission and reception, UART1 also provides full modem control handshake. The UART3 also has an infrared mode for infrared communication.
This design uses RS232 level conversion chip MAX232 to realize serial communication of UART0. URAT1 uses SP3243ECA conversion chip to convert the signal into RS232 level, which can be connected with MODEM to control MODEM dialing, communication and so on. The circuit diagram is shown in Figure 2.
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