【正文】 s functions are set by the AT89C51 receiving the entered data. In order to save the external resistor, the 16 keyboard is used, and the keyboard codes are defined as: 07H, 0FH, 17H, 1FH, 27H, 2FH. The order can be read out by reading the code instruction. HD7279A is connected to the AT89S51 in serial mode and only 4 ports are need. As shown in Fig. 6, DIG0~DIG5 and DP are respectively the column lines and row line ports of the six keys which achieve keyboard monitoring, decoding and key codes identification. F. Alarm Circuit In order to simplify the circuit and convenient debugging, a 5V automatic buzzer is used in the alarm circuit [8]. And this make the software programming simplified. As shown in Fig. 7, it is controlled by the PNP transistor 9012 whose base is connected to the pin of the AT89C51. When the temperature exceeds the upper and lower limit value, the output low level which makes the transistor be on and then an alarm is given by the buzzer. G. Drive Circuit A step motor is used as the drive device to control the temperature. The fourphase and eightbeat pulse distribution mode is used to drive motor and the 安徽理工大學(xué)畢業(yè)設(shè)計(jì)外文文獻(xiàn)翻譯 11 simple delay program is used to handle the time interval between the pulses to obtain different rotational speed. There are two output states for the step motor. One: when the temperature is over the upper value, the motor rotates reversely (to low the temperature), while when lower than the lower limit value, the motor rotates normally (to raise the temperature)。 it is passed from the program to the outside world. In this case the program may call an output subroutine which supervises the operation of the interface and performs the scaling numbers which may be needed for digitaltoanalog converter(DAC). This subroutine passes information in turn to an output device which produces a corresponding electrical signal, which could be converted into analog form using a DAC. Finally the signal is conditioned(usually amplified) to a form suitable for operating an actuator. The signals used within microputer circuits are almost always too small to be connected directly to the outside world” and some kind of interface must be used to translate them to a more appropriate form. The design of section of interface circuits is one of the most important tasks facing the engineer wishing to apply microputers. We have seen that in microputers information is represented as discrete patterns of bits。 temperature 1 INTRODUCTION Temperature is a very important parameter in human life. In the modern society, temperature control (TC) is not only used in industrial production, but also widely used in other fields. With the improvement of the life quality, we can find the TC appliance in hotels, factories and home as well. And the trend that TC will better serve the whole society, so it is of great significance to measure and control the temperature. Based on the AT89C51 and temperature sensor DS18B20, this system controls the condition temperature intelligently. The temperature can be set discretionarily within a certain range. The system can show the time on LCD, and save monitoring data。 安徽理工大學(xué)畢業(yè)設(shè)計(jì)外文文獻(xiàn)翻譯 1 Design of the Temperature Control System Based on AT89C51 ABSTRACT The principle and functions of the temperature control system based on micro controller AT89C51 are studied, and the temperature measurement unit consists of the 1Wire bus digital temperature sensor DS18B20. The system can be expected to detect the preset temperature, display time and save monitoring data. An alarm will be given by system if the temperature exceeds the upper and lower limit value of the temperature which can be set discretionarily and then automatic control is achieved, thus the temperature is achieved monitoring intelligently within a certain range. Basing on principle of the system, it is easy to make a variety of other nonlinear control systems so long as the software design is reasonably changed. The system has been proved to be accurate, reliable and satisfied through field practice. KEYWORDS: AT89C51。 and automatically control the temperature when the condition temperature exceeds the upper and lower limit value. By doing so it is to keep the temperature unchanged. The system is of high antijamming, high control precision and flexible design。 this digital form is most useful when the microputer is to be connected to equipment which can only be switched on or off, where each bit might represent the state of a switch or actuator. To solve realworld problems, a microcontroller must have more than just a CPU, a program, and a data memory. In addition, it must contain hardware allowing the CPU to access information from the outside world. Once the CPU gathers information and processes the data, it must also be able to effect change on some portion of the outside world. These hardware devices, called peripherals, are the CPU’ s window to the outside. The most basic form of peripheral available on microcontrollers is the general 安徽理工大學(xué)畢業(yè)設(shè)計(jì)外文文獻(xiàn)翻譯 8 purpose I70 port. Each of the I/O pins can be used as either an input or an output. The function of each pin is determined by setting or clearing corresponding bits in a corresponding data direction register during the initialization stage of a program. Each output pin may be driven to either a logic one or a logic zero by using CPU instructions to pin may be viewed (or read.) by the CPU using program instructions. Some type of serial unit is included on microcontrollers to allow the CPU to municate bitseria