【正文】 化后它將自動定時到操作完成。 DSl820 在與微處理器連接時僅需要一條接口線即可實(shí)現(xiàn)微處理器與 DSl820 的雙向通訊。 (5)可測量的溫度范圍從 55℃ 到 +125℃ ，增量值 0. 5℃ ；華氏溫度范圍從 67 到 +257，增量值 0． 9。測量結(jié)果以 9 位數(shù)字量方式串行傳送。圖中低溫度系數(shù)品振的振蕩頻率受溫度影響很小，用于產(chǎn)生同定頻率的脈沖信號送給計數(shù)器 l。計數(shù)器 l 對低溫度系數(shù)晶振產(chǎn)生的脈沖信號進(jìn)行減法計數(shù)，當(dāng)計數(shù)器 1 的預(yù)置值減到 O 時，溫度計數(shù)器的值將加l，計數(shù)器 l 的預(yù)置值將被重新裝人，計數(shù)器 l 重新開始對低溫度系數(shù)晶振產(chǎn)生的脈沖信號進(jìn)行計數(shù)，如此循環(huán)直到計數(shù)器 2 計數(shù)到 O 時，停止溫度寄存器的累加，此時溫度寄存器中的數(shù)值即為所測溫度。寄生電源方式有三個好處： 1）進(jìn)行遠(yuǎn)距離測溫時，無需本地電源。 外部電源供電方式：在外部電源供電方式下， DS18B20 工作電源由 VDD 引腳接入，此時 I/O 線不需要強(qiáng)上拉，不存在電源電流不足的問題，可以保證轉(zhuǎn)換精度，同時在總線上理論可以掛接任意多個 DS18B20 傳感器，組成多點(diǎn)測溫系統(tǒng)。若要組成多點(diǎn)溫度檢測系統(tǒng)，可在單片機(jī)的同一根 I/O 口線上，以相同的連接方法并聯(lián)多片 DS18B20 芯片。 風(fēng)扇電路 當(dāng)所測的溫度高于 80 攝氏度時，啟動風(fēng)扇電路。多功能溫度檢測顯示系統(tǒng)軟件主要包括：函數(shù)聲明、延遲時間函數(shù)、 DS18B20 初始化函數(shù)、讀出 DS18B20 當(dāng)前的溫度、溫度數(shù)據(jù)轉(zhuǎn)化成液晶字符顯示等程序。本系統(tǒng)采用的是 DALLAS 公司推出的數(shù)字式溫度傳感器 DS18B20，無需外加 A／ D 即可輸出數(shù)字量，把溫度信號直接轉(zhuǎn)換成串行數(shù)字信號供微機(jī)處理。 本文摘譯自： atmel AT89C51 中文資料 DATSHEET 規(guī)格書 DS18B20 的英文數(shù)據(jù)手冊 DS18B20 Programmable Resolution 1Wire Digital Thermometer 中原工學(xué)院信息商務(wù)學(xué)院外文 翻譯 9 Based on SCM multifunctional temperature testing system design preface With the development of society and the technological progress, people pay more and more attention to the importance of temperature detection and display. Temperature detection and status display technology and equipment has been widely applied in industries, products on the market emerge in endlessly. Temperature testing and also gradually adopt the automatic control technology to realize the monitor. This topic is a temperature testing and status of the monitoring system. System solutions This system USES the monolithic integrated circuit AT89C51 as this system. The whole system, the hardware circuit including power supply circuit, sensor, the temperature display circuit circuit, upper alarm circuit . The alarming circuit can be measured in upper temperature range, screaming voice alarm. The basic principle for the temperature control DSl8B20: when the temperature signal acquisition to after temperature signal sent to handle, AT89C51 temperature to LCD screen, SCM according to initialize the upper temperature setting, namely, if the judgement of temperature than the highest temperature cooling fan is started, If the temperature is less than the lowest temperature setting on alarm device. The system hardware design （ 1） AT89C51 SCM are introduced The AT89C51 is a lowpower, highperformance CMOS 8bit microputer with 4K bytes of Flash programmable and erasable read only memory (PEROM) and 128 bytes of data randomaccess memory(RAM). The device is manufactured using ATMEL Co.’s highdensity nonvolatile memory technology and is patible with the industrystandard MCS51 instruction set and pinout. 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 Flash on a monolithic chip, the ATMEL Co.’s AT89C51 is a powerful microputer which provides a highlyflexible and costeffective solution to many embedded control applications. Features: Fully static operation: 0 Hz to 24 MHz Two 16bit Timer/Counters VCC: Supply voltage Port 2: Port 2 is an 8bit bidirectional I/O port with internal pull ups. The Port 2 output buffers can sink/source four TTL inputs. When 1s are written to Port 2 pins they are pulled high by the internal pull ups and can be used as inputs. As inputs, Port 2 pins that are externally being pulled low will source current (IIL) because of the internal pull ups. Port 2 emits the highorder address byte during fetches from external program memory and during accesses to external data memory which uses 16bit addresses (MOVX DPTR). In this application, it uses strong internal pull ups when emitting 1s. During accesses to external data memory which uses 8bit addresses (MOVX RI). Port 2 emits the contents of the P2 Special Function Register. Port 2 also receives the highorder address bits and some control signals during Flash programming and verification. PSEN ： Program Store Enable is the read strobe to external program memory. When the AT89C51 is executing code from external program memory, PSEN is activated twice each machine cycle, except that two PSEN activations are skipped during each access to external data memory. Ready/ BUSY : The progress of byte programming can also be monitored by the RDY/BSY output signal. is pulled low after ALE goes high during programming to indicate BUSY. is pulled high again when programming is done to indicate READY. Oscillator Characteristics： XTAL1 and XTAL2 are the input and output, respectively, of an inverting amplifier which can be configured for use as an onchip oscillator. Either a quartz crystal or ceramic resonator may be used. To drive the device from an external clock source, XTAL2 should be left unconnected while XTAL1 is driven. There are no requirements on the duty cycle of the external clock signal, since the input to the internal clocking circuitry is through a divide by two flip trigger, but minimum and maximum voltage high and low time specifications must be observed. Idle Mode： In idle mode, the CPU puts itself to sleep while all the onchip peripherals remain active. The mode is invoked by software. The content of the onchip RAM and all the special functions registers remain unchanged during this mode. The idle mode can be terminated by any enabled interrupt or by a hardware reset. It should be noted that when idle is terminated by a hardware reset, the device normally resumes program execution, from where it left off, up to two machine cycles before the internal reset algorithm takes control. On