2.1 Processor Selection

IS220UCSAH1A Embedded controller is widely used in industry. Because the processor is the core of the controller, different types of processors have different application bases. Embedded processors are mainly divided into four categories: embedded microprocessor, embedded microcontroller, embedded DSP, and embedded system-on-chip SOC[3]. However, with the increasingly high requirements for embedded control systems in industrial control, the control algorithm is becoming more and more complex. At present, ARM microprocessor is the most widely used status quo. ARM7 is mainly used in industrial control, Internet equipment, network and modem equipment, mobile phones and other multimedia and embedded applications. ARM9 is mainly used in wireless devices, instruments, security systems, set-top boxes, high-end printers, digital cameras and digital cameras, etc. ARM10E series of microprocessors are mainly used in next-generation wireless devices, digital consumer products, imaging equipment, process control, graphics and information systems, etc. In this paper, Philips LPC2880 chip is used as processor, which is a member of ARM7 series. It has the following characteristics :8kB cache,64kB SRAM, working frequency up to 60MHz; External memory controller supports flash,SRAM,ROM, and SDRAM; 2 32-bit timers with optional pre-divider; Boot ROM allows flash code and external code to be executed. flash programming via USB is allowed.

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2.2 Power circuit design

IS220UCSAH1A The operating voltage of the core chip is 1.8V and the operating voltage of the I/0 interface is 3.3V. The system should be designed as a 3.3V application system based on high voltage. The implementation method is as follows: use a 220V to 9V transformer to convert office power into 9V DC power supply, and then the 9V DC power supply input from another power supply interface, and use diode to prevent power reverse connection, after secondary filtering, through the LM2575 switching power supply chip produced by the United States National Semiconductor Company to stabilize the power supply to 5V. Finally, the 5V power supply is output to 3.3V and 1.8V voltage through the low voltage difference power supply chip. The low-voltage differential power supply chip can be SPX1117 series chips SPX1117M3-3.3 and SPX1117M3-1.8 produced by Sipex Company, which is characterized by large output current, high output voltage precision and high stability. Accuracy is plus or minus 1%. It also has current limitation and thermal protection.

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2.3 System clock circuit and reset circuit design

IS220UCSAH1A In embedded control systems, clock circuit is often determined by the market. In industrial control systems, because of the high cost of machinery, clock circuit design in embedded systems can control the running time of machinery, forcing buyers to pay on time [4]. For the LPC2880 processor, the system clock can be adjusted through the internal PLL circuit to make the system run faster, which is the highest operating frequency of 60MHz. It can use external crystal oscillator or external clock source. If the on-chip PLL function is not used, the external crystal frequency is 1~30MHz and the external clock frequency is 1~50MHz; if the on-chip PLL function is used, the external crystal frequency is 10~25MHz and the external clock frequency is 10~25MHz. For the reset circuit, its design must make the system can be fully complex, to ensure the reliable operation of the system, because the LPC2880 chip has the characteristics of high speed, low power consumption, low working voltage leads to its low noise tolerance, so that it has higher requirements on the ripple, transient response performance of the power supply, the stability of the clock source, the reliability of the power supply monitoring. Reset circuit design must make the system can be fully reset, to ensure stable and reliable work in a variety of complex circumstances. The reset circuit in this paper uses CAT1025Jl-30, a dedicated power monitoring chip produced by CATALYST (reset threshold voltage is 3.0~3.15V).

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