外文翻譯---ds18b20 數(shù)字溫度計(jì)

1、<p><b>　　畢業(yè)論文(設(shè)計(jì))</b></p><p><b>　　文獻(xiàn)翻譯</b></p><p>　　本翻譯源自于： CNKI </p><p>　　畢業(yè)設(shè)計(jì)名稱： 基于單片機(jī)的轉(zhuǎn)速溫度智能測(cè)控系統(tǒng)設(shè)計(jì) </p><p>　　外文翻

2、譯名稱： DS18B20 溫度計(jì) </p><p>　　學(xué) 生 姓 名 ： 蔡信鵬 </p><p>　　院 (系)： 電子信息工程學(xué)院 </p><p>　　專 業(yè) 班 級(jí)

3、 ： 電氣10901 </p><p>　　指 導(dǎo) 教 師 ： 李金 </p><p>　　輔 導(dǎo) 教 師 ： 李金 </p><p>　　時(shí) 間 ：

4、 2013年2月 至 2013年6月 </p><p>　　DS18B20 數(shù)字溫度計(jì)</p><p>　　Ching Dai著，蔡信鵬譯</p><p><b>　　描述</b></p><p>　　DS18B20 數(shù)字溫度計(jì)提供9至12位溫度讀數(shù)，指示器件的溫度。</p><

5、;p>　　信息經(jīng)過(guò)單線接口送入DS18B20或送出，因此從中央處理器到DS18B20僅需連接一條（和地）。讀、寫和完成溫度變換所需的電源可以有數(shù)據(jù)線本身提供，而不需要外部電源。</p><p>　　因?yàn)槊恳粋€(gè)DS18B20有唯一的系列號(hào)，因此多個(gè)DS18B20可以存在于同一條單線總線上。這允許在許多不同的地方放置溫度靈敏器件。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(guò)程監(jiān)視

6、和控制中的溫度檢測(cè)。</p><p><b>　　特性</b></p><p>　　獨(dú)特的單線接口，只需一個(gè)接口引腳即可通信。</p><p>　　多點(diǎn)能力使分布式溫度檢測(cè)應(yīng)用得以簡(jiǎn)化。</p><p><b>　　不需要外部元件。</b></p><p>　　可用數(shù)據(jù)線供電

7、，提供3.0V到5.5V的電源。</p><p><b>　　不需備份電源。</b></p><p>　　測(cè)量范圍從-55°C 到+125°C，等效的華氏溫標(biāo)范圍是-67°F 到+257°F</p><p>　　以9到12位數(shù)字值方式讀出溫度。</p><p>　　在750毫秒內(nèi)把

8、12位溫度變換為數(shù)字。</p><p>　　用戶可定義的，非易失性的溫度警告設(shè)置。</p><p>　　告警搜索命令識(shí)別和尋址溫度在編定的極限之外的器件（溫度告警情況）。</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>　　引腳排列</b></p>

9、;<p><b>　　引腳說(shuō)明</b></p><p><b>　　GND – 地</b></p><p>　　DQ – 數(shù)字輸入輸出</p><p>　　VDD – 可選的VDD</p><p><b>　　NC – 不連接</b></p>

10、<p><b>　　詳細(xì)引腳說(shuō)明</b></p><p><b>　　綜述</b></p><p>　　圖1的方框圖表示DS18B20的主要部件。DS18B20有三個(gè)主要的數(shù)據(jù)部件：1）64為激光ROM，2）溫度靈敏元件，3）非易失性溫度告警觸發(fā)器TH和TL。器件從單線的通信線取得其電源，在信號(hào)線為高電平的時(shí)間周期內(nèi)，把能量貯存在內(nèi)部的

11、電容器中，在單信號(hào)線為低電平的時(shí)間期內(nèi)斷開此電源，直到信號(hào)線變?yōu)楦唠娖街匦陆由霞纳娙荩╇娫礊橹?，作為另一種可供選擇的方法，DS18B20也用外部5V電源供電。</p><p>　　與DS18B20的通信經(jīng)過(guò)一個(gè)單線接口。在單線接口情況下，在ROM操作未定建立之前不能使用存貯器和控制操作。主機(jī)必須首先提供五種ROM操作命令之一：1）讀ROM，2）符合ROM，3）搜索ROM,4)跳過(guò)ROM，5)告警搜索。這些命令

12、對(duì)每一個(gè)器件的64位激光ROM部分進(jìn)行操作。如果在單線上有許多器件，那么可以挑選出一個(gè)特定的器件，并給總線上的主機(jī)指示存在多少器件及其類型。在成功地執(zhí)行了ROM操作序列之后，可使用貯存2器和控制操作。然后主機(jī)可以提供六種存貯器和操作命令之一。</p><p>　　一個(gè)操作命令指示DS18B20完成溫度測(cè)量。改測(cè)量的結(jié)果放入DS18B20的高速暫存存貯器，通過(guò)發(fā)出讀暫存存儲(chǔ)器內(nèi)容的存儲(chǔ)器操作命令可以讀出此結(jié)果。每一

13、溫度告警觸發(fā)器TH和TL構(gòu)成一個(gè)字節(jié)的EPROM。如果不對(duì)DS18B20施加告警搜索命令，這些寄存器用作通用用戶存儲(chǔ)器。使用存儲(chǔ)器操作命令可以寫TH和TL。對(duì)這些寄存器的讀訪問(wèn)通過(guò)便簮存儲(chǔ)器。所以數(shù)據(jù)均以最低有效位在前的方式被讀寫。</p><p><b>　　單線總線系統(tǒng)</b></p><p>　　單線總線是一種具有一個(gè)總線主機(jī)和一個(gè)或若干個(gè)從機(jī)的系統(tǒng)。DS18B

14、20起從機(jī)的作用。這種總線系統(tǒng)的討論分為三個(gè)題目:硬件接法，處理順序，以及單線信號(hào)（信號(hào)類型與定時(shí)）。</p><p><b>　　硬件接法</b></p><p>　　根據(jù)定義，單線總線只有一根線：這一點(diǎn)很重要的，即線上的第一個(gè)器件能在適當(dāng)?shù)臅r(shí)間驅(qū)動(dòng)該總線。為了做到這一點(diǎn)第一個(gè)連接到總線上的器件必須具有漏極開路或三態(tài)輸出。DS18B20的單線接口。多站總線由單線總線

15、和多個(gè)與之相連的從屬器件組成。單線總線要求近似等于5 k.</p><p>　　單線總線的空閑狀態(tài)是高電平。不管任何原因，如果執(zhí)行需要被掛起，那么，若要重新恢復(fù)執(zhí)行，總線必須保持在空閑狀態(tài)。如果不滿足這一點(diǎn)且總線保持在低電平時(shí)間大于480微秒，那么總線上所有的器件均被復(fù)位。</p><p><b>　　硬件連接圖</b></p><p><

16、;b>　　處理順序</b></p><p>　　經(jīng)過(guò)單線總線接口訪問(wèn)DS18B20的協(xié)議如下：</p><p><b>　　初始化</b></p><p><b>　　ROM操作命令</b></p><p><b>　　存貯器操作命令</b></p>

17、;<p><b>　　處理/數(shù)據(jù)</b></p><p><b>　　初始化</b></p><p>　　單線總線上的所有處理均從初始化序列開始。初始化序列包括總線主機(jī)發(fā)出一復(fù)位脈沖，接著由從屬器件送出存在脈沖。</p><p><b>　　ROM操作命令</b></p>

18、<p>　　一旦總線主機(jī)檢測(cè)到從屬器件的存在，他便可以發(fā)出器件ROM操作命令之一。所有ROM操作命令均由8位長(zhǎng)，這些命令列表如下：</p><p>　　讀ROM [33H]</p><p>　　此命令允許總線主機(jī)讀DS18B20的8位產(chǎn)品系列編碼，唯一的48位序列號(hào)，以及8位的CRC。此命令只能在總線上僅有一個(gè)DS18B20得情況下可以使用。如果總線上存在多于一個(gè)得從屬器件，那

19、么所有從片企圖同時(shí)發(fā)送時(shí)將發(fā)生數(shù)據(jù)沖突的現(xiàn)象。</p><p>　　符合ROM [55h]</p><p>　　符合ROM命令。后繼以64位的ROM數(shù)據(jù)序列，允許總線主機(jī)對(duì)多點(diǎn)總線上的DS18B20尋址。只有與64位ROM序列嚴(yán)格相符的DS18B20才能對(duì)后繼的存貯器操作命令作出響應(yīng)。所有與64位ROM序列不符的從片將等待復(fù)位脈沖。此命令在總線數(shù)據(jù)上有單個(gè)或多個(gè)器件的情況下均可使用。<

20、;/p><p>　　跳過(guò)ROM[CCh]</p><p>　　在單點(diǎn)總線系統(tǒng)中，此命令通過(guò)允許總線主機(jī)不提供64位ROM編碼而訪問(wèn)存儲(chǔ)器操作來(lái)節(jié)省時(shí)間。如果在總線上存在多于一個(gè)得從屬器件而且在跳過(guò)ROM命令之后發(fā)出讀命令，那么由于多個(gè)從片同時(shí)發(fā)送數(shù)據(jù)，會(huì)在總線上發(fā)生數(shù)據(jù)沖突</p><p>　　搜索ROM[F0h]</p><p>　　當(dāng)系統(tǒng)開始

21、工作時(shí)，總線主機(jī)可能不知道單線總線上的器件個(gè)數(shù)或者不知道其64位ROM編碼。搜索ROM命令允許總線主機(jī)使用一種消去處理來(lái)識(shí)別總線上的所有從片的64位ROM編碼。</p><p><b>　　告警搜索[ECh]</b></p><p>　　此命令的流程與搜索ROM命令相同。但是，僅在最近一次溫度測(cè)量出現(xiàn)告警的情況下，DS18B20才對(duì)此命令作出響應(yīng)。告警的條件定義為溫度

22、高于TH或低于TL。只要DS18B20一上電，告警條件就保持在設(shè)置狀態(tài)，直到另一次溫度測(cè)量告警。</p><p><b>　　ROM搜索舉例</b></p><p>　　ROM搜索過(guò)程是簡(jiǎn)單三步過(guò)程的重復(fù)：讀一位，讀核位的補(bǔ)碼，然后寫所需的那一位的值。總線主機(jī)在ROM的每一位上完成這一簡(jiǎn)單的三步過(guò)程。在全部過(guò)程完成之后，總線主機(jī)便知道一個(gè)器件中ROM的內(nèi)容，器件中其余

23、的數(shù)以及他們的ROM編碼可以游另外一個(gè)過(guò)程來(lái)識(shí)別。</p><p>　　以下ROM搜索過(guò)程的例子假設(shè)四個(gè)不同的器件連接到同一條單線總線上。四個(gè)器件的ROM數(shù)據(jù)如下所示：</p><p>　　ROM1 00110101…</p><p>　　ROM2 10101010…</p><p>　　ROM3 11110101…</p>&

24、lt;p>　　ROM4 00010001…</p><p><b>　　搜索過(guò)程如下：</b></p><p>　　1.總線主機(jī)通過(guò)發(fā)出復(fù)位脈沖開始初始化序列，從屬器件通過(guò)發(fā)出同時(shí)的存在脈沖作出響應(yīng)。</p><p>　　2.然后總線主機(jī)在單線總線上發(fā)出搜索人ROM命令。</p><p>　　3.總線主機(jī)從單線過(guò)程

25、中讀一位。每一器件通過(guò)把他們各自ROM數(shù)據(jù)的第一位的值放到單線總線上來(lái)作出響應(yīng)。ROM1和ROM4:將把一個(gè)0放在單線總線上，即，把它拉至低電平。ROM2和3通過(guò)使總線停留在高電平而把1放在單線總線上。結(jié)果是線上所有器件的邏輯與，因此總線主機(jī)接收到一個(gè)0.總線主機(jī)讀另一位。因此搜索ROM數(shù)據(jù)命令正在執(zhí)行，所以單線總線上所有器件通過(guò)把各自ROM數(shù)據(jù)第一位的補(bǔ)碼放到單線總線上來(lái)對(duì)這第二個(gè)讀作出響應(yīng)。ROM1和ROM2把1放在單總線上，使之處

26、于高電平。ROM2和ROM3把0放在單線上，因此他將被拉至低電平。對(duì)于第一個(gè)ROM數(shù)據(jù)位的補(bǔ)碼總線主機(jī)觀察到得仍是一個(gè)0.總線主機(jī)便可決定單線總線上有一些第一位為0的器件和一些第一位為1的器件。</p><p>　　4.總線主機(jī)寫一個(gè)0.在這次搜索過(guò)程的其余部分，將不選擇ROM2和ROM3，僅留下連接到單線總線的ROM1和ROM4。</p><p>　　5.總線主機(jī)再執(zhí)行兩次讀，并在一個(gè)1

27、位之后接收到一個(gè)0位，這表示所有還連接在總線上的器件的第二個(gè)ROM數(shù)據(jù)位為0.</p><p>　　6.總線主機(jī)接著寫一個(gè)0，使ROM1和ROM4二者保持連接。</p><p>　　7.總線主機(jī)執(zhí)行兩次連讀，并接收到兩次0數(shù)據(jù)位。這表示連接著的器件ROM數(shù)據(jù)的第三位都是1數(shù)據(jù)位和0數(shù)據(jù)位。</p><p>　　8.總線主機(jī)寫一個(gè)數(shù)據(jù)位。這將不選擇ROM1而把ROM4

28、作為唯一仍連接著的器件加以保留。</p><p>　　9.總線主機(jī)讀ROM4的ROM數(shù)據(jù)位的剩余部分，而且訪問(wèn)需要的部件。這就完成了第一個(gè)過(guò)程并且唯一的識(shí)別單線總線上的部件。</p><p>　　10.總線主機(jī)通過(guò)重復(fù)步驟1至7開始一個(gè)新的ROM搜索序列。</p><p>　　11.總線主機(jī)寫一個(gè)1，這將不與ROM4發(fā)生聯(lián)系，而唯一的與ROM1仍保持著聯(lián)系。<

29、/p><p>　　12.總線主機(jī)對(duì)于ROM1讀出ROM位的剩余部分而且，如果需要的話，與內(nèi)部邏輯通信。這就完成了第二個(gè)ROM搜索過(guò)程，在其中ROM中的另一個(gè)被找到。</p><p>　　13.總線主機(jī)通過(guò)重復(fù)步驟1至3開始一次新的ROM搜索。</p><p><b>　　注意下述內(nèi)容：</b></p><p>　　在第一次R

30、OM搜索過(guò)程中，總線主機(jī)知道一個(gè)單線器件的唯一的ID號(hào)。取得部件唯一ROM編碼的時(shí)間為：</p><p>　　960us+(8+3×64)us=13.16ms</p><p>　　因此總線主機(jī)每秒鐘能夠識(shí)別75個(gè)不同的單線器件。</p><p>　　DS18B20 Digital Thermometer</p><p><b&

31、gt;　　Ching Dai</b></p><p>　　DESCRIPTION</p><p>　　The DS18B20 Digital Thermometer provides 9 to 12-bit (configurable) temperature readings which indicate the temperature of the device.</

32、p><p>　　Information is sent to/from the DS18B20 over a 1-Wire interface, so that only one wire (and ground) needs to be connected from a central microprocessor to a DS18B20. Power for reading, writing, and perf

33、orming temperature conversions can be derived from the data line itself with no need for an external power source.</p><p>　　Because each DS18B20 contains a unique silicon serial number, multiple DS18B20s can

34、 exist on the same 1-Wire bus. This allows for placing temperature sensors in many different places. Applications where this feature is useful include HVAC environmental controls, sensing temperatures inside buildings, e

35、quipment or machinery, and process monitoring and control.</p><p><b>　　FEATURES</b></p><p>　　Unique 1-Wire interface requires only one port pin for communication</p><p>

36、　　Multidrop capability simplifies distributed temperature sensing applications</p><p>　　Requires no external components</p><p>　　Can be powered from data line. Power supply range is 3.0V to 5.5V

37、</p><p>　　Zero standby power required</p><p>　　Measures temperatures from -55°C to+125°C. Fahrenheit equivalent is -67°F to +257°F</p><p>　　Thermometer resolutio

38、n is programmable from 9 to 12 bits</p><p>　　Converts 12-bit temperature to digital word in 750 ms (max.)</p><p>　　User-definable, nonvolatile temperature alarm settings</p><p>　　Al

39、arm search command identifies and addresses devices whose temperature is outside of programmed limits (temperature alarm condition)</p><p>　　Applications include thermostatic controls, industrial systems, co

40、nsumer products,thermometers, or any thermally sensitivesystem.</p><p>　　PIN ASSIGNMENT</p><p>　　PIN DESCRIPTION</p><p>　　GND - Ground</p><p>　　DQ - Data In/Out</p&g

41、t;<p>　　VDD - Power Supply Voltage</p><p>　　NC - No Connect</p><p>　　DETAILED PIN DESCRIPTION </p><p><b>　　OVERVIEW</b></p><p>　　The block diagram of

42、 Figure 1 shows the major components of the DS18B20. The DS18B20 has four main data components: 1) 64-bit lasered ROM, 2) temperature sensor, 3) nonvolatile temperature alarm triggers TH and TL. The device derives its po

43、wer from the 1-Wire communication line by storing energy on an internal capacitor during periods of time when the signal line is high and continues to operate off this power source during the low times of the 1-Wire line

44、 until it returns high to replenish the </p><p>　　DS18B20 BLOCK DIAGRAM Figure 1</p><p>　　Communication to the DS18B20 is via a 1-Wire port. With the 1-Wire port, the memory and control function

45、s will not be available before the ROM function protocol has been established. The master must first provide one of five ROM function commands: 1) Read ROM, 2) Match ROM, 3) Search ROM, 4) Skip ROM, or 5) Alarm Search. T

46、hese commands operate on the 64-bit lasered ROM portion of each</p><p>　　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

47、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 funct

48、ion commands.</p><p>　　One control function command instructs the DS18B20 to perform a temperature measurement. The result of this measurement will be placed in the DS18B20’s scratch-pad memory, and may be r

49、ead by issuing a memory function command which reads the contents of the scratchpad memory. The temperature alarm triggers TH and TL consist of 1 byte EEPROM each. If the alarm search command is not applied to the DS18B2

50、0, these registers may be used as general purpose user memory. The scratchpad also contains a co</p><p>　　1-WIRE BUS SYSTEM</p><p>　　The 1-Wire bus is a system which has a single bus master and

51、one or more slaves. The DS18B20 behaves as a slave. The discussion of this bus system is broken down into three topics: hardware configuration, transaction sequence, and 1-Wire signaling (signal types and timing).</p&

52、gt;<p>　　HARDWARE CONFIGURATION</p><p>　　The 1-Wire bus has only a single line by definition; it is important that each device on the bus be able to drive it at the appropriate time. To facilitate thi

53、s, each device attached to the 1-Wire bus must have open drain or 3-state outputs. The 1-Wire port of the DS18B20 (DQ pin) is open drain with an internal circuit equivalent to that shown in Figure 9. A multidrop bus cons

54、ists of a 1-Wire bus with multiple slaves attached. The 1-Wire bus requires a pullup resistor of approximately 5 k?.</p><p>　　The idle state for the 1-Wire bus is high. If for any reason a transaction needs

55、to be suspended, the bus MUST be left in the idle state if the transaction is to resume. Infinite recovery time can occur between bits so long as the 1-Wire bus is in the inactive (high) state during the recovery period

56、. If this does not occur and the bus is left low for more than 480 s, all components on the bus will be reset.</p><p>　　HARDWARE CONFIGURATION </p><p>　　TRANSACTION SEQUENCE</p><p>

57、　　The protocol for accessing the DS18B20 via the 1-Wire port is as follows:</p><p>　　_ Initialization</p><p>　　_ ROM Function Command</p><p>　　_ Memory Function Command</p>&

58、lt;p>　　_ Transaction/Data</p><p>　　INITIALIZATION</p><p>　　All transactions on the 1-Wire bus begin with an initialization sequence. The initialization sequence consists of a reset pulse tran

59、smitted by the bus master followed by presence pulse(s) transmitted by the slave(s). The presence pulse lets the bus master know that the DS18B20 is on the bus and is ready to operate. For more details, see the “1-Wire S

60、ignaling” section.</p><p>　　ROM FUNCTION COMMANDS</p><p>　　Once the bus master has detected a presence, it can issue one of the five ROM function commands. All ROM function commands are 8 bits l

61、ong. A list of these commands follows (refer to flowchart in Figure 5)</p><p>　　Read ROM [33h]</p><p>　　This command allows the bus master to read the DS18B20’s 8-bit family code, unique 48-bit

62、serial number, and 8-bit CRC. This command can only be used if there is a single DS18B20 on the bus. If more than one slave is present on the bus, a data collision will occur when all slaves try to transmit at the same t

63、ime (open drain will produce a wired AND result).</p><p>　　Match ROM [55h]</p><p>　　The match ROM command, followed by a 64-bit ROM sequence, allows the bus master to address a specific DS18B20

64、on a multidrop bus. Only the DS18B20 that exactly matches the 64-bit ROM sequence will respond to the following memory function command. All slaves that do not match the 64-bit ROM sequence will wait for a reset pulse. T

65、his command can be used with a single or multiple devices on the bus.</p><p>　　Skip ROM [CCh]</p><p>　　This command can save time in a single drop bus system by allowing the bus master to access

66、 the memory functions without providing the 64-bit ROM code. If more than one slave is present on the bus and a Read command is issued following the Skip ROM command, data collision will occur on the bus as multiple slav

67、es transmit simultaneously (open drain pulldowns will produce a wired AND result).</p><p>　　Search ROM [F0h]</p><p>　　When a system is initially brought up, the bus master might not know the num

68、ber of devices on the 1-Wire bus or their 64-bit ROM codes. The search ROM command allows the bus master to use a process of elimination to identify the 64-bit ROM codes of all slave devices on the bus.</p><p&

69、gt;　　Alarm Search [ECh]</p><p>　　The flowchart of this command is identical to the Search ROM command. However, the DS18B20 will respond to this command only if an alarm condition has been encountered at the

70、 last temperature measurement. An alarm condition is defined as a temperature higher than TH or lower than TL. The alarm condition remains set as long as the DS18B20 is powered up, or until another temperature measuremen

71、t reveals a non-alarming value. For alarming, the trigger values stored in EEPROM are taken into account. </p><p>　　Example of a ROM Search</p><p>　　The ROM search process is the repetition of a

72、 simple three-step routine: read a bit, read the complement of the bit, then write the desired value of that bit. The bus master performs this simple, three-step routine on each bit of the ROM. After one complete pass, t

73、he bus master knows the contents of the ROM in one device. The remaining number of devices and their ROM codes may be identified by additional passes.</p><p>　　The following example of the ROM search process

74、 assumes four different devices are connected to the same 1-Wire bus. The ROM data of the four devices is as shown:</p><p>　　ROM1 00110101...</p><p>　　ROM2 10101010...</p><p>　　ROM

75、3 11110101...</p><p>　　ROM4 00010001...</p><p>　　The search process is as follows:</p><p>　　1. The bus master begins the initialization sequence by issuing a reset pulse. The slave

76、devices respond by issuing simultaneous presence pulses.</p><p>　　2. The bus master will then issue the Search ROM command on the 1-Wire bus.</p><p>　　3. The bus master reads a bit from the 1-W

77、ire bus. Each device will respond by placing the value of the first bit of their respective ROM data onto the 1-Wire bus. ROM1 and ROM4 will place a 0 onto the 1-Wire bus, i.e., pull it low. ROM2 and ROM3 will place a 1

78、onto the 1-Wire bus by allowing the line to stay high. The result is the logical AND of all devices on the line, therefore the bus master sees a 0. The bus master reads another bit. Since the Search ROM data command is b

79、eing executed,</p><p>　　all of the devices on the 1-Wire bus respond to this second read by placing the complement of the first bit of their respective ROM data onto the 1-Wire bus. ROM1 and ROM4 will place

80、a 1 onto the 1-Wire, allowing the line to stay high. ROM2 and ROM3 will place a 0 onto the 1-Wire, thus it will be pulled low. The bus master again observes a 0 for the complement of the first ROM data bit. The bus maste

81、r has determined that there are some devices on the 1-Wire bus that have a 0 in the first positio</p><p>　　4. The bus master writes a 0. This deselects ROM2 and ROM3 for the remainder of this search pass,<

82、;/p><p>　　leaving only ROM1 and ROM4 connected to the 1-Wire bus.</p><p>　　5. The bus master performs two more reads and receives a 0-bit followed by a 1-bit. This indicates that all devices still

83、coupled to the bus have 0s as their second ROM data bit.</p><p>　　6. The bus master then writes a 0 to keep both ROM1 and ROM4 coupled.</p><p>　　7. The bus master executes two reads and receives

84、 two 0-bits. This indicates that both 1-bits and 0-bits exist as the 3rd bit of the ROM data of the attached devices.</p><p>　　8. The bus master writes a 0-bit. This deselects ROM1, leaving ROM4 as the only

85、device still</p><p>　　connected.</p><p>　　9. The bus master reads the remainder of the ROM bits for ROM4 and continues to access the part if</p><p>　　desired. This completes the fir

86、st pass and uniquely identifies one part on the 1-Wire bus.</p><p>　　10. The bus master starts a new ROM search sequence by repeating steps 1 through 7.</p><p>　　11. The bus master writes a 1-bi

87、t. This decouples ROM4, leaving only ROM1 still coupled.</p><p>　　12. The bus master reads the remainder of the ROM bits for ROM1 and communicates to the underlying logic if desired. This completes the secon

88、d ROM search pass, in which another of the ROMs was found.</p><p>　　13. The bus master starts a new ROM search by repeating steps 1 through 3.</p><p><b>　　NOTE:</b></p><p&

89、gt;　　The bus master learns the unique ID number (ROM data pattern) of one 1-Wire device on each ROM</p><p>　　Search operation. The time required to derive the part’s unique ROM code is:</p><p>