【正文】 lly with external devices. Using a bit serial format instead of bitparallel format requires fewer I/O pins to perform the munication function, which makes it less expensive, but slower. Serial transmissions are performed either synchronously or asynchronously. 3 SYSTEM GENERAL DESIGN The hardware block diagram of the TC is shown in Fig. 1. The system hardware includes the micro controller, temperature detection circuit, keyboard control circuit, clock circuit, Display, alarm, drive circuit and external RAM. Based on the AT89C51, the DS18B20 will transfer the temperature signal detected to digital signal. And the signal is sent to the micro controller for processing. At last the temperature value is showed on the LCD 12232F. These steps are used to achieve the temperature detection. Using the keyboard interface chip HD7279 to set the temperature value, using the micro controller to keep a certain temperature, and using the LCD to show the preset value for controlling the temperature. In addition, the clock chip DS1302 is used to show time and the external RAM 6264 is used to save the monitoring data. An alarm will be given by buzzer in time if the temperature exceeds the upper and lower limit value of the temperature. HARDWARE DESIGN A. Micro controller The AT89C51 is a lowpower, highperformance CMOS 8bit micro controller with 4K bytes of insystem programmable Flash memory. The device is manufactured using At mel’s highdensity nonvolatile memory technology and is patible with the industrystandard 80C51 instruction set and pin out. The onchip Flash allows the program memory to be reprogrammed insystem or by a conventional nonvolatile memory programmer. By bining a versatile 8bit CPU with insystem programmable Flash on a monolithic chip, the At mel AT89C51 is a powerful micro controller which provides a highlyflexible and costeffective solution to many 安徽理工大學(xué)畢業(yè)設(shè)計(jì)外文文獻(xiàn)翻譯 9 embedded control applications. Minimum system of the micro controller is shown in Fig. 2. In order to save monitoring data, the 6264 is used as an external RAM. It is a static RAM chip, lowpower with 8K bytes memory. B. Temperature Detection Circuit The temperature sensor is the key part in the system. The Dallas DS18B20 is used, which supports the 1Wire bus interface, and the ONBOARD Patented is used internally. All the sensor parts and the converting circuit are integrated in integrated circuit like a transistor [1]. Its measure range is 55℃ ~125 ℃ , and the precision between 10℃ ~85℃ is 177。 besides not equals the preset value. Two: when the temperature is at somewhere between the two ends and equals the preset value, the motor stops. These steps are used to achieve the temperature control. In addition, the motor speed can also be adjusted by relative buttons. As shown in Fig. 8, the code data is input through ports A11~A8 (be ~) of the AT89C51 and inverted output by the inverter 74LS04. Finally it is amplified by the power amplifier 2803A to power the motor. SOFTWARE DESIGN According to the general design requirement and hardware circuit principle of the system, as well as the improvement of the program readability, transferability and the convenient debugging, the software design is modularized. The system flow mainly includes the following 8 steps: POST (Poweron selftest), system initiation, temperature detection, alarm handling, temperature control, clock chip DS18B20 operation, LCD and keyboard operation. The main program flow is shown in Fig. 9. Give a little analysis to the above 8 tasks, it is easy to find out that the last five tasks require the real time operation. But to the temperature detection it can be achieved with timer0 timing 1 second, that is to say temperature detection occurs per second. The system initiation includes global variable definition, RAM initiation, special function register initiation and peripheral equipment initiation. Global variable definition mainly finishes the interface definition of external interface chip connected to the AT89C51, and special definition of some memory units. RAM initiation mainly refers to RAM processing. For example when the system is electrified the time code will be stored in the internal unit address or the scintillation flag will be cleared. The special function register initiation includes loading the initial value of timer and opening the interrupt. For example, when the system is electrified the timer is initialized. The peripheral equipment initiation refers to set the initial value of peripheral equipment. For example, when the system is electrified, the LCD should be initialized, the startup display should be called, the temperature conversion mand should be issued firstly and the clock chip DS18B20 should also be initialized. The alarm handling is mainly the lowering and the raising of temperature to make the 安徽理工大學(xué)畢業(yè)設(shè)計(jì)外文文獻(xiàn)翻譯 12 temperature remain with the preset range. When the temperature is between the upper and the lower limit value, it goes to temperature control handling, that is to say the temperature need to be raised or lowered according to the preset value. By doing so make the condition temperature equal to the preset value and hence to reach the temperature target. 4 CONCLUSION The temperature control system has the advantages of friendly humanputer interaction interface, simple hardware, low cost, high temperature control precision (error in the range of 177。 the second pin serves as signal wire and the third is connected to the power. The second way is parasite power supply [5]. As the parasite power supply will lead to the plexity of the hardware circuit, the difficulty