ds18b20 單線溫度傳感器外文翻譯

1、<p>　　南 京 理 工 大 學(xué)</p><p>　　畢業(yè)設(shè)計(jì)(論文)外文資料翻譯</p><p>　　學(xué)院（系）： 機(jī)電一體化 </p><p>　　專 業(yè)： 電氣自動(dòng)化專業(yè) </p><p>　　姓 名： 周凌坤

2、 </p><p>　　學(xué) 號(hào)： 104910252036 </p><p>　　外文出處： http：//www.ourmpu.com </p><p>　　2012年4月5日 </p><p>　　附 件： 1.外文資料翻譯譯文；2.外文原文。&l

3、t;/p><p>　　注：請(qǐng)將該封面與附件裝訂成冊(cè)。</p><p>　　附件1：外文資料翻譯譯文</p><p>　　DS18B20 單線溫度傳感器</p><p><b>　　1．特征：</b></p><p>　　● 獨(dú)特的單線接口，只需 1 個(gè)接口引腳即可通信</p><

4、p>　　● 每個(gè)設(shè)備都有一個(gè)唯一的64位串行代碼存儲(chǔ)在光盤片上</p><p>　　● 多點(diǎn)能力使分布式溫度檢測(cè)應(yīng)用得以簡化</p><p>　　● 不需要外部部件</p><p>　　● 可以從數(shù)據(jù)線供電，電源電壓范圍為3.0V至5.5V</p><p>　　● 測(cè)量范圍從-55 ° C 至+125 ° C（-6

5、7 ° F至257 ° F），從-10℃至+85 ° C的精度為0.5 °C</p><p>　　● 溫度計(jì)分辨率是用戶可選擇的9至12位</p><p>　　● 轉(zhuǎn)換12位數(shù)字的最長時(shí)間是750ms</p><p>　　● 用戶可定義的 非易失性的溫度告警設(shè)置</p><p>　　● 告警搜索命令識(shí)別

6、和尋址溫度在編定的極限之外的器件 （溫度告警情況）</p><p>　　● 采用8引腳SO（150mil），8引腳SOP和3引腳TO - 92封裝</p><p>　　● 軟件與DS1822兼容</p><p>　　● 應(yīng)用范圍包括恒溫控制 工業(yè)系統(tǒng) 消費(fèi)類產(chǎn)品 溫度計(jì)或任何熱敏系統(tǒng)</p><p><b>　　2．簡介</b

7、></p><p>　　該DS18B20的數(shù)字溫度計(jì)提供9至12位的攝氏溫度測(cè)量，并具有與非易失性用戶可編程上限和下限報(bào)警功能。信息單線接口送入 DS1820 或從 DS1820 送出，因此按照定義只需要一條數(shù)據(jù)線（和地線）與中央微處理器進(jìn)行通信。它的測(cè)溫范圍從-55 °C到 +125 ° C，其中從-10 °C至+85 °C可以精確到0.5°C 。此外，D

8、S18B20可以從數(shù)據(jù)線直接供電（“寄生電源”），從而消除了供應(yīng)需要一個(gè)外部電源。</p><p>　　每個(gè) DS18B20 的有一個(gè)唯一的64位序列碼，它允許多個(gè)DS18B20s的功能在同一</p><p>　　1-巴士線。因此，用一個(gè)微處理器控制大面積分布的許多DS18B20s是非常簡單的。此特性的應(yīng)用范圍包括 HVAC、環(huán)境控制、建筑物、設(shè)備或機(jī)械內(nèi)的溫度檢測(cè)以及過程監(jiān)視和控制系統(tǒng)。

9、</p><p><b>　　3．綜述</b></p><p>　　64位ROM存儲(chǔ)設(shè)備的獨(dú)特序號(hào)。存貯器包含2個(gè)字節(jié)的溫度寄存器，它存儲(chǔ)來自溫度傳感器的數(shù)字輸出。此外，暫存器可以訪問的1個(gè)字節(jié)的上下限溫度告警觸發(fā)器（TH和TL）和1個(gè)字節(jié)的配置寄存器。配置寄存器允許用戶設(shè)置的溫度到數(shù)字轉(zhuǎn)換的分辨率為9，10，11或12位。TH，TL和配置寄存器是非易失性的，因此掉電

10、時(shí)依然可以保存數(shù)據(jù)。</p><p>　　該DS18B20使用Dallas的單總線協(xié)議，總線之間的通信用一個(gè)控制信號(hào)就可以實(shí)現(xiàn)。控制線需要一個(gè)弱上拉電阻，因?yàn)樗械脑O(shè)備都是通過3線或開漏端口連接（在DS18B20中用DQ引腳）到總線的。在這種總線系統(tǒng)中，微處理器（主設(shè)備）和地址標(biāo)識(shí)上使用其獨(dú)有的64位代碼。因?yàn)槊總€(gè)設(shè)備都有一個(gè)唯一的代碼，一個(gè)總線上連接設(shè)備的數(shù)量幾乎是無限的。 單總線協(xié)議，包括詳細(xì)的解釋命令和“時(shí)

11、間槽”，此資料的單總線系統(tǒng)部分包括這些內(nèi)容。</p><p>　　DS18B20的另一個(gè)特點(diǎn)是：沒有外部電源供電仍然可以工作。當(dāng)DQ引腳為高電平時(shí)，電壓是單總線上拉電阻通過DQ引腳供應(yīng)的。高電平信號(hào)也可以充當(dāng)外部電源，當(dāng)總線是低電平時(shí)供應(yīng)給設(shè)備電壓。這種從但總線提供動(dòng)力的方法被稱為“寄生電源“。作為替代電源，該DS18B20也可以使用連接到 VDD 引腳的外部電源供電。</p><p>　

12、　4．運(yùn)用 —— 測(cè)量溫度</p><p>　　該DS18B20的核心功能是它是直接輸出數(shù)字信號(hào)的溫度傳感器。該溫度傳感器的分辨率為用戶配置至9，10，11或12位，相當(dāng)于0.5° C，0.25° C，0.125 ° C和0.0625° C的增量。其中傳感器默認(rèn)為12位。該DS18B20在低功耗空閑狀態(tài)；啟動(dòng)溫度測(cè)量和模數(shù)轉(zhuǎn)換，主機(jī)必須發(fā)出一個(gè)轉(zhuǎn)換命令。轉(zhuǎn)換后，所產(chǎn)生的數(shù)據(jù)

13、存儲(chǔ)在內(nèi)存中的2比特溫度寄存器中，DS18B20返回其空閑狀態(tài)。如果DS18B20是由外部電源供電的，主機(jī)可以發(fā)出“讀時(shí)隙”，轉(zhuǎn)換后，通過發(fā)送低電平T命令和DS18B20將響應(yīng)，同時(shí)溫度轉(zhuǎn)換繼續(xù)進(jìn)行，當(dāng)轉(zhuǎn)換完成時(shí)變?yōu)楦唠娖?。如果DS18B20的是寄生電源供電的，在整個(gè)溫度轉(zhuǎn)換過程中此通知技術(shù)不能使用，因?yàn)榭偩€必須變?yōu)楦唠娖??？偩€需要寄生電源供電將在此資料的DS18B20驅(qū)動(dòng)部分將詳細(xì)介紹。</p><p>　　D

14、S18B20的輸出溫度數(shù)據(jù)為標(biāo)準(zhǔn)攝氏度;對(duì)于華氏溫度的應(yīng)用，必須通過查表或運(yùn)用轉(zhuǎn)換方法。溫度數(shù)據(jù)在溫度寄存器存儲(chǔ)為一個(gè)16位符號(hào)擴(kuò)展位和2位的補(bǔ)碼。該標(biāo)志位（S）表示溫度的正負(fù)符號(hào)位：為正數(shù)時(shí)S = 0，為負(fù)數(shù)時(shí)S = 1。如果是DS18B20配置為12位分辨率，在溫度寄存器的所有位將包含有效數(shù)據(jù)。對(duì)于11位分辨率，位0是未定義的。對(duì)于10位分辨率，位1和0是未定義的。對(duì)于9位分辨率，位2，1和0是未定義的。表2給出了輸出數(shù)字?jǐn)?shù)據(jù)和相應(yīng)

15、的12位分辨率溫度讀數(shù)轉(zhuǎn)換例子。</p><p>　　5．運(yùn)用 - 報(bào)警信號(hào)</p><p>　　DS18B20溫度轉(zhuǎn)換完成后，溫度值與用戶定義的2個(gè)報(bào)警觸發(fā)值存儲(chǔ)在1個(gè)字節(jié)的TH和TL寄存器。符號(hào)位（S）表示溫度值的正負(fù)： S = 0時(shí)為正值， S = 1為負(fù)值。TH和TL寄存器是非易失（EEPROM），因此他們將保留設(shè)備掉電時(shí)的數(shù)據(jù)。 TH和TL可通過暫存器中字節(jié)2和3獲得，此內(nèi)容在本

16、數(shù)據(jù)表內(nèi)存部分解釋。</p><p>　　6．TH和TL寄存器格式</p><p>　　只有溫度寄存器4中的11位用于和TL的比較中，由于TH和TL都是 8位寄存器。如果測(cè)量溫度低于或等于TL或超過TH，報(bào)警情況存在而且報(bào)警標(biāo)志將設(shè)置在DS18B20的內(nèi)部。每個(gè)溫度測(cè)量后，這個(gè)標(biāo)志位將被更新，因此，如果報(bào)警條件消失，下一個(gè)溫度轉(zhuǎn)換后，該標(biāo)志位將被關(guān)閉。主設(shè)備可以通過搜索ECH命令檢查總線上

17、所有DS18B20s報(bào)警標(biāo)志位的狀態(tài)。任何有設(shè)置報(bào)警標(biāo)志位的DS18B20s將響應(yīng)命令，所以主設(shè)備可以決定到底是哪個(gè)DS18B20s在經(jīng)歷一個(gè)報(bào)警條件。如果報(bào)警的情況存在，TH和TL設(shè)置已經(jīng)改變了，另一個(gè)溫度轉(zhuǎn)換應(yīng)該去驗(yàn)證報(bào)警條件。</p><p>　　7．DS18B20的驅(qū)動(dòng)</p><p>　　該傳感器DS18B20可以用外部電源接VDD端供電，或者它可以工作在“寄生電源”模式下，這種

18、模式允許DS18B20在沒有外部電源下工作。寄生電源在遠(yuǎn)程或者空間受限情況下感溫是非常有用的。寄生功率控制電路，其中當(dāng)總線引腳為高電平時(shí)，力部門宿舍從DS18B201通過連接單總線的DQ端“偷”電。當(dāng)總線是高電平或者總線是低電平，而一些能量存貯在CPP中來提供電源，“偷”來的電位DS18B20提供驅(qū)動(dòng)。</p><p>　　當(dāng)DS18B20在寄生電源模式下使用時(shí)，VDD引腳必須接地。在寄生電源模式下，單總線和CP

19、P可以提供足夠的電流給DS18B20的大部分操作，只要指定的時(shí)間和電壓的要求得到滿足（參考本數(shù)據(jù)手冊(cè)DC電氣特性和AC電氣特性章節(jié)）。</p><p>　　然而，當(dāng)DS18B20溫度轉(zhuǎn)換或復(fù)制暫存器的數(shù)據(jù)到EEPROM時(shí)，工作電流可高達(dá)1.5毫安。這個(gè)電流會(huì)導(dǎo)致無法接受的電壓下降，整個(gè)單總線電阻壓降減小，更多的電流可以由寄生電源供應(yīng)。為了確保DS18B20有足夠的電流供應(yīng)，無論正在發(fā)生溫度轉(zhuǎn)換或復(fù)制暫存器的數(shù)據(jù)到

20、EEPROM，單總線都必須接一個(gè)強(qiáng)上拉電阻。</p><p>　　單總線必須在轉(zhuǎn)換T[44h]或暫存器復(fù)制[48H]命令發(fā)出后， 10秒內(nèi)（最大）轉(zhuǎn)換到強(qiáng)上拉狀態(tài)，而且總線必須在轉(zhuǎn)換（tconv）或數(shù)據(jù)傳輸（twr = 10ms）期間通過上拉保持高電平。在單總線上拉使能時(shí)，其他活動(dòng)不能發(fā)生。該DS18B20的也可以采用的連接外部電源到VDD腳上的傳統(tǒng)方法。</p><p>　　這種方法的優(yōu)

21、點(diǎn)是不需要MOSFET的上拉， 而且單總線可以在進(jìn)行溫度轉(zhuǎn)換時(shí)間自由地進(jìn)行其他操作。在+100℃以上的高溫時(shí)不推薦使用寄生電源，因?yàn)樵谶@些溫度下存在較高泄漏電流，DS18B20可能無法維持通信。對(duì)于像在這種高溫下的使用，強(qiáng)烈建議由一個(gè)DS18B20的外部電源供電。在某些情況下，總線主機(jī)可能不知道DS18B20s是外部電源還是寄生電源供電。主機(jī)需要這些信息來確定是否強(qiáng)大的總線上拉應(yīng)在溫度轉(zhuǎn)換時(shí)使用。要獲得這些信息，主機(jī)可以在 “閱讀時(shí)段”

22、 一個(gè)讀取電源[B4h]命令后，發(fā)出一個(gè)跳過ROM[CCh]命令。在讀時(shí)隙，寄生電源給DS18B20s供電將把總線電平拉低，外部供電時(shí)DS18B20s將會(huì)讓總線仍然保持高電平。如果總線拉低，主機(jī)知道在溫度轉(zhuǎn)換期間它必須提供單總線強(qiáng)上拉。</p><p>　　8．64位激光ROM</p><p>　　每一 DS1820 包括一個(gè)唯一的 64 位長的 ROM 編碼。開紿的 8 位是單線產(chǎn)品系列

23、編碼：28h，接著的 48 位是唯一的系列號(hào)。最重要的8位是開始 56 位 CRC位，從56位的ROM端計(jì)算而來。CRC比特的詳細(xì)內(nèi)容將在CRC概述一章中介紹。64位ROM代碼和相關(guān)ROM功能控制邏輯使DS18B20作為使用協(xié)議的單線設(shè)備的運(yùn)作，單總線系統(tǒng)的數(shù)據(jù)表部分詳細(xì)介紹了這個(gè)協(xié)議。</p><p><b>　　9．存貯器</b></p><p>　　DS1820

24、的存貯器那樣被組織 存貯器由一個(gè)高速暫存 便箋式 RAM、一個(gè)存貯高溫度和低溫度和觸發(fā)器 TH 和 TL的非易失性電可擦除 E2RAM和存儲(chǔ)配置寄存器組成。請(qǐng)注意，如果DS18B20的報(bào)警功能不使用，TH和TL寄存器可以作為通用存儲(chǔ)器。 DS18B20的功能命令部分詳細(xì)敘述了所有內(nèi)存的命令。暫存器的字節(jié)0和字節(jié)1分別包含LSB和MSB溫度寄存器。這些字節(jié)是只讀的。字節(jié)2和3提供是提供接入的TH和TL寄存器。字節(jié)4包含配置寄存器數(shù)據(jù)，數(shù)據(jù)

25、表配置寄存器部分詳細(xì)解釋了它的內(nèi)容。字節(jié)5，6和7是保留供內(nèi)部使用的設(shè)備，不能被覆蓋，當(dāng)被讀到時(shí)，這些字節(jié)將返回1秒。8字節(jié)暫存器是只讀的，并且包含了循環(huán)冗余校驗(yàn)碼，通過暫存器的0到7字節(jié)。DS18B20使用在CRC生成一節(jié)中描述的方法生成該CRC。數(shù)據(jù)寫入字節(jié)2，3，暫存器4使用寫入暫存[4Eh]指令;數(shù)據(jù)必須傳輸?shù)紻S18B20以最低有效位開始的第2字節(jié)。為了驗(yàn)證數(shù)據(jù)的完整性，數(shù)據(jù)被寫入后暫存器可以讀?。ㄊ褂脭?shù)據(jù)讀取暫存器[與Beh

26、]命令）。當(dāng)讀取暫存器，數(shù)據(jù)是從最低有效位的0字節(jié)開始的。要傳送的TH，TL和配置數(shù)據(jù)從暫存器到EEPROM</p><p><b>　　10．配置寄存器</b></p><p>　　暫存存儲(chǔ)器的第四字節(jié)包含配置寄存器。用戶可以使用該寄存器的R0和R1的位置DS18B20的轉(zhuǎn)換分辨率。這些位默認(rèn)是R0和R1都等于1（12位）的分辨率。請(qǐng)注意，兩者之間是有直接的分辨率和

27、轉(zhuǎn)換時(shí)間的對(duì)比。第7位，并在配置寄存器0至4位是保留供內(nèi)部使用的設(shè)備，不能被覆蓋，這些位被讀出時(shí)將返回1秒。</p><p><b>　　11.CRC生成</b></p><p>　　CRC字節(jié)是DS18B20的64位ROM代碼的一部分，在暫存器的第9比特。CRC的代碼是由前56位的ROM代碼計(jì)算出的，并處在ROM中最重要的字節(jié)。暫存器中的CRC代碼是由儲(chǔ)存器中的數(shù)據(jù)

28、計(jì)算出來的，因此它變化時(shí)，在暫存器中的數(shù)據(jù)也會(huì)變化。CRCs提供總線主機(jī)數(shù)據(jù)驗(yàn)證方法，當(dāng)主機(jī)從DS18B20讀取數(shù)據(jù)時(shí)。為了驗(yàn)證數(shù)據(jù)已被正確讀取，總線主機(jī)必須從接收到的數(shù)據(jù)中重新計(jì)算CRC，然后比較此值無論是ROM代碼（為ROM讀）或暫存器的CRC（為暫存器讀?。?。如果計(jì)算出的CRC與讀到的CRC匹配，說明已收到的數(shù)據(jù)準(zhǔn)確無誤。 CRC的值比較，是否繼續(xù)運(yùn)作完全由總線主機(jī)決定。如果DS18B20的CR（ROM或暫存器）與由總線主機(jī)產(chǎn)生的

29、值不匹配，DS18B20中沒有任何電路阻止命令序列的進(jìn)程。由總線主機(jī)產(chǎn)生的價(jià)值電路。CRC的同等多項(xiàng)式函數(shù)（ROM或暫存器）是：CRC = X8+ X5 + X4+ 1 總線主機(jī)可以重新計(jì)算CRC，然后使用多項(xiàng)式發(fā)生器與從DS18B20得到用的CRC值進(jìn)行比較。該電路由一個(gè)移位寄存器和XOR門組成，移位寄存器初始化為0。從暫存器最低有效位或0字節(jié)的最低有效位的開始，每次一</p><p>　　附件2：外文原文（復(fù)

30、印件）</p><p>　　DS18B20 Single - wire temperature sensor</p><p>　　1. FEATURES</p><p>　　● Unique 1-Wireinterface requires only one port pin for communication </p><p>　　●

31、Each device has a unique 64-bit serial code stored in an onboard ROM</p><p>　　● Multidrop capability simplifies distributed temperature sensing applications </p><p>　　● Requires no external com

32、ponents </p><p>　　● Can be powered from data line. Power supply range is 3.0V to 5.5V </p><p>　　● Measures temperatures from –55°C to +125°C (–67°F to +257°F) 0.5C accuracy

33、from –10°C to +85°C </p><p>　　● Thermometer resolution is user-selectable from 9 to 12 bits </p><p>　　● Converts temperature to 12-bit digital word in 750ms (max.) </p><p>

34、;　　● User-definable nonvolatile (NV) alarm settings </p><p>　　● Alarm search command identifies and addresses devices whose temperature is </p><p>　　outside of programmed limits (temperature ala

35、rm condition) </p><p>　　● Available in 8-pin SO (150mil), 8-pin SOP, and 3-pin TO-92 packages </p><p>　　● Software compatible with the DS1822 </p><p>　　● Applications include therm

36、ostatic controls, industrial systems, consumer</p><p>　　products, thermometers, or any thermally sensitive</p><p>　　2. DESCRIPTION </p><p>　　The DS18B20 Digital Thermometer provides

37、 9 to 12–bit centigrade temperature measurements and has an alarm function with nonvolatile user-programmable upper and lower trigger points. The DS18B20 communicates over a 1-Wire bus that by definition requires only o

38、ne data line (and ground) for communication with a central microprocessor. It has an operating temperature range of –55°C to +125°Cand is accurate to 0.5C over the range of –10°C to +85°C. In addition

39、, the DS18B20 can derive powerdirectly f</p><p>　　Each DS18B20 has a unique 64-bit serial code, which allows multiple DS18B20s to function on the same 1–wire bus; thus, it is simple to use one microprocessor

40、 to control many DS18B20s distributed over a large area. Applications that can benefit from this feature include HVAC environmental controls, temperature monitoring systems inside buildings, equipment or machinery, and p

41、rocess monitoring and control systems.</p><p>　　3. OVERVIEW</p><p>　　Figure 1 shows a block diagram of the DS18B20, and pin descriptions are given in Table 1. The 64-bit ROM stores the device’s

42、unique serial code. The scratchpad memory contains the 2-byte temperature register that stores the digital output from the temperature sensor. In addition, the scratchpad provides access to the 1-byte upper and lower ala

43、rm trigger registers (TH and TL), and the 1-byte configuration register. The configuration register allows the user to set the resolution of the temperatur</p><p>　　The DS18B20 uses Dallas’ exclusive 1-Wire

44、bus protocol that implements bus communication using one control signal. The control line requires a weak pullup resistor since all devices are linked to the bus via a 3-state or open-drain port (the DQ pin in the case o

45、f the DS18B20). In this bus system, the microprocessor (the master device) identifies and addresses devices on the bus using each device’s unique 64-bit code. Because each device has a unique code, the number of devices

46、that can be addres</p><p>　　Another feature of the DS18B20 is the ability to operate without an external power supply. Power is instead supplied through the 1-Wire pullup resistor via the DQ pin when the bus

47、 is high. The high bus signal also charges an internal capacitor (CPP), which then supplies power to the device when the bus is low. This method of deriving power from the 1-Wire bus is referred to as “parasite power.” A

48、s an alternative, the DS18B20 may also be powered by an external supply on VDD。</p><p>　　4. OPERATION — MEASURING TEMPERATURE</p><p>　　The core functionality of the DS18B20 is its direct-to-digi

49、tal temperature sensor. The resolution of the temperature sensor is user-configurable to 9, 10, 11, or 12 bits, corresponding to increments of 0.5 C, 0.25 C, 0.125 C, and 0.0625 C, respectively. The default resolution at

50、 power-up is 12-bit. The DS18B20 powers-up in a low-power idle state; to initiate a temperature measurement and A-to-D conversion, the master must issue a Convert T [44h] command. Following the conversion, the resulting

51、t</p><p>　　The DS18B20 output temperature data is calibrated in degrees centigrade; for Fahrenheit applications, a lookup table or conversion routine must be used. The temperature data is stored as a 16-bit

52、sign-extended two’s complement number in the temperature register (see Figure 2). The sign bits (S) indicate if the temperature is positive or negative: for positive numbers S = 0 and for negative numbers S = 1. If the D

53、S18B20 is configured for 12-bit resolution, all bits in the temperature register wil</p><p>　　5. OPERATION — ALARM SIGNALING</p><p>　　After the DS18B20 performs a temperature conversion, the tem

54、perature value is compared to the user-defined two’s complement alarm trigger values stored in the 1-byte TH and TL registers (see Figure 3). The sign bit (S) indicates if the value is positive or negative: for positive

55、numbers S = 0 and for negative numbers S = 1. The TH and TL registers are nonvolatile (EEPROM) so they will retain data when the device is powered down. TH and TL can be accessed through bytes 2 and 3 of the scratchpad a

56、</p><p>　　6. TH AND TL REGISTER FORMAT Figure 3</p><p>　　Only bits 11 through 4 of the temperature register are used in the TH and TL comparison since TH and TL are 8-bit registers. If the measu

57、red temperature is lower than or equal to TL or higher than TH, an alarm condition exists and an alarm flag is set inside the DS18B20. This flag is updated after every temperature measurement; therefore, if the alarm con

58、dition goes away, the flag will be turned off after the next temperature conversion. The master device can check the alarm flag status of all </p><p>　　7. POWERING THE DS18B20 </p><p>　　The DS1

59、8B20 can be powered by an external supply on the VDD pin, or it can operate in “parasite power” mode, which allows the DS18B20 to function without a local external supply. Parasite power is very useful for applications

60、that require remote temperature sensing or that are very space constrained. Figure 1 shows the DS18B20’s parasite-power control circuitry, which “steals” power from the 1-Wire bus via the DQ pin when the bus is high. The

61、 stolen charge powers the DS18B20 while the bus is hi</p><p>　　When the DS18B20 is used in parasite power mode, the VDD pin must be connected to ground. In parasite power mode, the 1-Wire bus and CPP can pr

62、ovide sufficient current to the DS18B20 for most operations as long as the specified timing and voltage requirements are met (refer to the DC ELECTRICAL CHARACTERISTICS and the AC ELECTRICAL CHARACTERISTICS sections of

63、 this data sheet).</p><p>　　However, when the DS18B20 is performing temperature conversions or copying data from the scratchpad memory to EEPROM, the operating current can be as high as 1.5mA. This current c

64、an cause an unacceptable voltage drop across the weak 1-Wire pullup resistor and is more current than can be supplied by CPP. To assure that the DS18B20 has sufficient supply current, it is necessary to provide a strong

65、 pullup on the 1-Wire bus whenever temperature conversions are taking place or data is being copied f</p><p>　　The 1-Wire bus must be switched to the strong pullup within 10s (max) after a Convert T [44h] or

66、 Copy Scratchpad [48h] command is issued, and the bus must be held high by the pullup for the duration of the conversion (tconv) or data transfer (twr = 10ms). No other activity can take place on the 1-Wire bus while th

67、e pullup is enabled. The DS18B20 can also be powered by the conventional method of connecting an external power supply to the VDD pin, as shown in Figure 5. </p><p>　　The advantage of this method is that the

68、 MOSFET pullup is not required, and the 1-Wire bus is free to carry other traffic during the temperature conversion time. The use of parasite power is not recommended for temperatures above +100C since the DS18B20 may no

69、t be able to sustain communications due to the higher leakage currents that can exist at these temperatures. For applications in which such temperatures are likely, it is strongly recommended that the DS18B20 be powered

70、by an external power</p><p>　　8. 64-BIT LASERED ROM CODE </p><p>　　Each DS18B20 contains a unique 64–bit code (see Figure 6) stored in ROM. The least significant 8 bits of the ROM code contain t

71、he DS18B20’s 1-Wire family code: 28h. The next 48 bits contain a unique serial number. The most significant 8 bits contain a cyclic redundancy check (CRC) byte that is calculated from the first 56 bits of the ROM code. A

72、 detailed explanation of the CRC bits is provided in the CRC GENERATION section. The 64-bit ROM code and associated ROM function control logic allow the </p><p>　　9. MEMORY </p><p>　　The DS18B20

73、’s memory is organized as shown in Figure 7. The memory consists of an SRAM scratchpad with nonvolatile EEPROM storage for the high and low alarm trigger registers (TH and TL) and configuration register. Note that if the

74、 DS18B20 alarm function is not used, the TH and TL registers can serve as general-purpose memory. All memory commands are described in detail in the DS18B20 FUNCTION COMMANDS section. Byte 0 and byte 1 of the scratchpad

75、contain the LSB and the MSB of the temperature re</p><p>　　10. CONFIGURATION REGISTER </p><p>　　Byte 4 of the scratchpad memory contains the configuration register, which is organized as illustr

76、ated in Figure 8. The user can set the conversion resolution of the DS18B20 using the R0 and R1 bits in this register as shown in Table 3. The power-up default of these bits is R0 = 1 and R1 = 1 (12-bit resolution). Not

77、e that there is a direct tradeoff between resolution and conversion time. Bit 7 and bits 0 to 4 in the configuration register are reserved for internal use by the device and cannot b</p><p>　　11. CRC GENERAT

78、ION </p><p>　　CRC bytes are provided as part of the DS18B20’s 64-bit ROM code and in the 9thbyte of the scratchpad memory. The ROM code CRC is calculated from the first 56 bits of the ROM code and is contain

79、ed in the most significant byte of the ROM. </p><p>　　The scratchpad CRC is calculated from the data stored in the scratchpad, and therefore it changes when the data in the scratchpad changes. The CRC provid

80、e the bus master with a method of data validation when data is read from the DS18B20. </p><p>　　To verify that data has been read correctly, the bus master must re-calculate the CRC from the received data an

81、d then compare this value to either the ROM code CRC (for ROM reads) or to the scratchpad CRC (for scratchpad reads).If the calculated CRC matches the read CRC, the data has been received error free. The comparison of CR