【正文】 erate on the 64–bit lasered ROM portion of each device and can single out a specific device if many are present on the 1–Wire line as well as indicate to the Bus Master how many and what types of devices are present. After a ROM function sequence has been successfully executed, the memory and control functions are accessible and the master may then provide any one of the six memory and control function mands. One control function mand instructs the DS1820 to perform a temperature measurement. The result of this measurement will be placed in the DS1820’s scratchpad memory, and may be read by issuing a memory function mand which reads the contents of the scratchpad memory. The temperature alarm triggers TH and TL consist of one byte EEPROM each. If the alarm search mand is not applied to the DS1820, these registers may be used as general purpose user memory. Writing TH and TL is done using a memory function mand. Read access to these registers is through the scratchpad. All data is read and written least significant bit block diagram (Figure 1) shows the parasite powered circuitry. This circuitry “steals” power whenever the I/O or VDD pins are high. I/O will provide sufficient power as long as the specified timing and voltage requirements are met (see the section titled “1–Wire Bus System”). The advantages of parasite power are two–fold:1) by parasiting off this pin, no local power source is needed for remote sensing of temperature, 2) the ROM may be read in absence of normal power. In order for the DS1820 to be able to perform accurate temperature conversions, sufficient power must be provided over the I/O line when a temperature conversion is taking place. Since the operating current of the DS1820 is up to 1 mA, the I/O line will not have sufficient drive due to the 5K pull–up resistor. This problem is particularly acute if several DS1820’s are on the same I/O and attempting to convert simultaneously.There are two ways to assure that the DS1820 has sufficient supply current during its active conversion cycle. The first is to provide a strong pull–up on the I/O line whenever temperature conversions or copies to the E2 memory are taking place. This may be acplished by using a MOSFET to pull the I/O line directly to the power supply as shown in Figure 2. The I/O line must be switched over to the strong pull–up within 10 ms maximum after issuing any protocol that involves copying to the E2 memory or initiates temperature conversions. When using the parasite power mode, the VDD pin must be tied to ground. Another method of supplying current to the DS1820 is through the use of an external power supply tied to the VDD pin, as shown in Figure 3. The advantage to this is that the strong pull–up is not required on the I/O line, and the bus master need not be tied up holding that line high during temperature conversions. This allows other data traffic on the 1–Wire bus during the conversion time. In addition, any number of DS1820’s may be placed on the 1–Wire bus, and if they all use external power, they may all simultaneously perform temperature conversions by issuing the Skip ROM mand and then issuing the Convert T mand. Note that as long as the external power supply is active, the GND pin may not be floating. The use of parasite power is not remended above 100176。C in 176。C LSB, yielding the following 9–bit format:The most significant (sign) bit is duplicated into all of the bits in the upper MSB of the two–byte temperature register in memory. This “sign–extension” yields the 16–bit temperature readings as shown in Table 1. Higher resolutions may be obtained by the following procedure. First, read the temperature, and truncate the 176。 it will send back a “1” if it is powered from the VDD pin. If the master receives a “0”, it knows that it must supply the strong pull–up on the I/O line during temperature conversions. See “Memory Command Functions” section for more detail on this mand protocol.OPERATION – MEASURING TEMPERATUREThe DS1820 measures temperature through the use of an on–board proprietary temperature measurement technique. A block diagram of the temperature measurement circuitry is shown in Figure 4. The DS1820 measures temperature by counting the number of clock cycles that an oscillator with a low temperature coefficient goes through during a gate period determined by a high temperature coefficient oscillator. The counter is preset with a base count that corresponds to –55176。附　錄 溫度、相對(duì)濕度檢測(cè)儀的電路原理圖外文資料原文DS1820FEATURES? Unique 1–WireTM interface requires only one port pin for munication? Multidrop capability simplifies distributed temperature sensing applications? Requires no external ponents? Can be powered from data line? Zero standby power required? Measures temperatures from –55176。參考文獻(xiàn)[1] ,1989[2] 華成英, 童詩白. 模擬電子技術(shù)基礎(chǔ)第三版. 北京: 高等教育出版社, . [3] 謝光忠、蔣亞東等. 2000,19(4):2933[4] :機(jī)械工業(yè)出版社,1993[5] 、系統(tǒng)配置與接口技術(shù).[6] 陳寶江,翟涌,.[7] 喻評(píng)，：化學(xué)工業(yè)出版社，2006[8] ：北京航空航天大學(xué)出版社。由于采用了測(cè)量范圍廣、精度高、響應(yīng)速度快的電容式濕度傳感器來進(jìn)行濕度采樣，使用溫度補(bǔ)償、線性化處理的方法提高檢測(cè)精度，因此該檢測(cè)儀基本上達(dá)到技術(shù)指標(biāo)中對(duì)相對(duì)濕度測(cè)量精度和分辨力的要求。 通過該芯片來輔助LED的顯示，就能夠節(jié)約I/O口資源，又能夠減少軟件的開支，所以比較適合本設(shè)計(jì)的需要。SAOMIAO: MOV A,R1 MOV R2,08HXS: JB ,XS1 CLR AJMP CLKXS1: SETB CLK: CLR NOP SETB RR A DJNZ R2,XSRET本段程序就是將一個(gè)單元8位二進(jìn)制數(shù)送出的子程序，,。 167。如果（ff1）的值大于0，說明實(shí)測(cè)頻率在濕度頻率曲線的第一段內(nèi)，這時(shí)的環(huán)境濕度值：RH=△RH (f f0)/( f1 f0)。因?yàn)榫€性化處理的過程中需要將實(shí)測(cè)頻率與fn進(jìn)行多次比較。 中斷計(jì)數(shù)是將波源輸入到單片機(jī)的中斷入口中去，通過檢測(cè)一段時(shí)間內(nèi)中都的次數(shù)也能夠檢測(cè)出波形的頻率，具體工作原理入下，先用一個(gè)定時(shí)器來實(shí)現(xiàn)計(jì)時(shí)功能，然后開中斷，讓中斷工作在邊沿觸發(fā)狀態(tài)，這樣中斷就可以對(duì)高低變換的頻率波形進(jìn)行計(jì)數(shù)，本設(shè)計(jì)中是來檢測(cè)波形頻率的所以最好的計(jì)一秒鐘采樣一次，同樣的問題，單片機(jī)必須的計(jì)若干次數(shù)才采集一個(gè)中斷次數(shù)，這樣才可以實(shí)現(xiàn)一秒采集數(shù)據(jù)。但是由上面的關(guān)系，可以采用軟件的方法進(jìn)行溫度補(bǔ)償和線性化處理，來實(shí)現(xiàn)高精度地測(cè)量相對(duì)濕度。從圖33可以看出，對(duì)于不同的環(huán)境濕度，振蕩頻率的溫度補(bǔ)償系數(shù)也是不同的。單片機(jī)中數(shù)據(jù)的處理全部是用二進(jìn)制數(shù)表示的，這種表示方法不適合我們平時(shí)的讀數(shù)習(xí)慣，還得先將十六進(jìn)制數(shù)轉(zhuǎn)變?yōu)閷?duì)應(yīng)的十進(jìn)制數(shù)來顯示，此時(shí)一次溫度檢測(cè)才算完成，程序返回進(jìn)行重復(fù)檢測(cè)來實(shí)現(xiàn)實(shí)時(shí)檢測(cè)環(huán)境溫度。STC12C5410AD 系列帶A/D 轉(zhuǎn)換的單片機(jī)在P1 口，有8 路10 位高速A/D 轉(zhuǎn)換器, 速度可達(dá)100KHz。儀表的應(yīng)用軟件系統(tǒng)配置有專用的服務(wù)子程序完成此項(xiàng)工