計(jì)算機(jī)專業(yè)畢業(yè)設(shè)計(jì)外文翻譯--ds1820

1、<p><b>　　外文資料原文</b></p><p><b>　　DS1820</b></p><p><b>　　FEATURES</b></p><p>　　? Unique 1–WireTM interface requires only one port pin for comm

2、unication</p><p>　　? Multidrop capability simplifies distributed temperature sensing applications</p><p>　　? Requires no external components</p><p>　　? Can be powered from data line

3、</p><p>　　? Zero standby power required</p><p>　　? Measures temperatures from –55°C to +125°C in 0.5°C increments. Fahrenheit equivalent is –67°F to +257°F in 0.9°F

4、 increments</p><p>　　? Temperature is read as a 9–bit digital value.</p><p>　　? Converts temperature to digital word in 200 ms (typ.)</p><p>　　? User–definable, nonvolatile temperat

5、ure alarm settings</p><p>　　? Alarm search command identifies and addresses devices whose temperature is outside of programmed limits (temperature alarm condition)</p><p>　　? Applications includ

6、e thermostatic controls, industrial systems, consumer products, thermometers, or any thermally sensitive system</p><p>　　DESCRIPTION</p><p>　　The DS1820 Digital Thermometer provides 9–bit temper

7、ature readings which indicate the temperature of the device. Information is sent to/from the DS1820 over a 1–Wire interface, so that only one wire (and ground) needs to be connected from a central microprocessor to a DS1

8、820. Power for reading, writing, and performing temperature conversions can be derived from the data line itself with no need for an external power source. Because each DS1820 contains a unique silicon serial number, mu

9、ltiple D</p><p>　　DETAILED PIN DESCRIPTION</p><p><b>　　OVERVIEW</b></p><p>　　The block diagram of Figure 1 shows the major components of the DS1820. The DS1820 has three

10、 main data components:</p><p>　　1) 64–bit lasered ROM,</p><p>　　2) temperature and sensor, </p><p>　　3) nonvolatile temperature alarm triggers TH and TL. </p><p>　　The

11、device derives its power 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 tim

12、es of the 1–Wire line until it returns high to replenish the parasite (capacitor) supply. As an alternative, the DS1820 may also be powered from an external 5 volts supply.</p><p>　　Communication to the DS18

13、20 is via a 1–Wire port. With the 1–Wire port, the memory and control functions will not be available before the ROM function protocol has been established. The master must first provide one of five ROM function commands

14、: 1) Read ROM, 2) Match ROM, 3) Search ROM, 4) Skip ROM, or 5) Alarm Search. These commands operate 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

15、line as well as indicate to the Bus</p><p>　　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 m

16、emory and control function commands. One control function command 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 rea

17、d by issuing a memory function command which reads the contents of the scratchpad memory. The temperature alarm trigge</p><p>　　The advantages of parasite power are two–fold:</p><p>　　1) by para

18、siting off this pin, no local power source is needed for remote sensing of temperature, </p><p>　　2) the ROM may be read in absence of normal power. In order for the DS1820 to be able to perform accurate tem

19、perature 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 driv

20、e 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.</p><p>　　There are two ways to assure that the DS1820 ha

21、s 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 accomplis

22、hed 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

23、 to the E2 me</p><p>　　ROM protocol, then issuing the read power supply command. After this command is issued, the master then issues read time slots.</p><p>　　The DS1820 will send back “0” on t

24、he 1–Wire bus if it is parasite powered; 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 convers

25、ions. See “Memory Command Functions” section for more detail on this command protocol.</p><p>　　OPERATION – MEASURING TEMPERATURE</p><p>　　The DS1820 measures temperature through the use of an o

26、n–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 oscilla

27、tor 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 –55°C. If the counter rea

28、ches zero </p><p>　　If the gate period is still not finished, then this process repeats. The slope accumulator is used to compensate for the non–linear behavior of the oscillators over temperature, yielding

29、a high resolution temperature measurement. This is done by changing the number of counts necessary for the counter to go through for each incremental degree in temperature. To obtain the desired resolution, therefore, bo

30、th the value of the counter and the number of counts per degree C (the value of the slope acc</p><p>　　Internally, this calculation is done inside the DS1820 to provide 0.5°C resolution. The temperature

31、 reading is provided in a 16–bit, sign–extended two’s complement reading. Table 1 describes the exact relationship of output data to measured temperature. The data is transmitted serially over the 1–Wire interface. The D

32、S1820 can measure temperature over the range of –55°C to +125°C in 0.5°C increments. For Fahrenheit usage, a lookup table or conversion factor must be used.</p><p>　　Note that temperature is r

33、epresented in the DS1820 in terms of a 1/2°C LSB, yielding the following 9–bit format:</p><p>　　The most significant (sign) bit is duplicated into all of the bits in the upper MSB of the two–byte temper

34、ature 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 0.5

35、°C bit (the LSB) from the read value. This value is TEMP_READ. The value left in the counter may then be read. This value is the count remaining (COUNT_REMAIN) after the gate</p><p>　　1–WIRE BUS SYSTEM&

36、lt;/p><p>　　The 1–Wire bus is a system which has a single bus master and one or more slaves. The DS1820 behaves as a slave. The discussion of this bus system is broken down into three topics: hardware configura

37、tion, transaction sequence, and 1–Wire signaling (signal types and timing).</p><p>　　HARDWARE CONFIGURATION The 1–Wire bus has only a single line by definition; it is important that each device on the bus be

38、 able to drive it at the appropriate time. To facilitate this, each device attached to the 1–Wire bus must have open drain or 3–state outputs.</p><p>　　The 1–Wire port of the DS1820 (I/Opin) is open drain wi

39、th an internal circuit equivalent to that shown in Figure 9. A multidrop bus consists of a 1–Wire bus with multiple slaves attached. The 1–Wire bus requires a pullup resistor of approximately 5KW.</p><p>　　T

40、he idle state for the 1–Wire bus is high. If for any reason a transaction needs 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 lo

41、ng as the 1–Wire bus is in the inactive (high) state during the recovery period. If this does not occur and the bus is left low for more than 480 ms, all components on the bus will be reset. TRANSACTION SEQUENCE</p>

42、;<p>　　The protocol for accessing the DS1820 via the 1–Wire port is as follows:</p><p>　　? Initialization</p><p>　　? ROM Function Command</p><p>　　? Memory Function Command&l

43、t;/p><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

44、 pulse transmitted by the bus master followed by presence pulse(s) transmitted by the slave(s).</p><p>　　The presence pulse lets the bus master know that the DS1820 is on the bus and is ready to operate. For

45、 more details, see the “1–Wire Signaling” 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 RO

46、M function commands are 8–bits long. A list of these commands follows (refer to flowchart in Figure 6):</p><p>　　Read ROM [33h]</p><p>　　This command allows the bus master to read the DS1820’s 8

47、–bit family code, unique 48–bit serial number,and 8–bit CRC. This command can only be used if there is a single DS1820 on the bus. If more than one slave is present on the bus, a data collision will occur when all slaves

48、 try to transmit at the same time (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

49、to address a specific DS1820 on a multidrop bus. Only the DS1820 that exactly matches the 64–bit ROM sequence will respond to the following memory function command. All slaves</p><p>　　that do not match the

50、64–bit ROM sequence will wait for a reset pulse. This 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 dr

51、op bus system by allowing the bus master to access 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, dat

52、a collision will occur on the bus as multiple slaves transmit simultaneously (open drain pulldowns will produce a wired AND result).</p><p>　　Search ROM [F0h]</p><p>　　When a system is initially

53、 brought up, the bus master might not know the number 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

54、of all slave devices</p><p>　　on the bus.</p><p><b>　　英文資料譯文</b></p><p><b>　　DS1820</b></p><p><b>　　特性：</b></p><p>　　&#

55、183;獨(dú)特的單線接口，只需1 個(gè)接口引腳即可通信；</p><p>　　·多點(diǎn)（multidrop）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><b>　　·可用數(shù)據(jù)線供電；</b></p><p>&l

56、t;b>　　·不需備份電源；</b></p><p>　　·測(cè)量范圍從-55至+125℃，增量值為0.5℃。等效的華氏溫度范圍是-67 F 至257 F，增量值為0.9 F；</p><p>　　·以9位數(shù)字值方式讀出溫度；</p><p>　　·在1秒（典型值）內(nèi)把溫度變換為數(shù)字；</p>&

57、lt;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>　　詳細(xì)說(shuō)明</b></p><

58、;p>　　DS1820有三個(gè)主要的數(shù)據(jù)部件：1）64位激光lasered ROM；2）溫度靈敏元件，和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╇娫礊橹埂Ｗ鳛榱硪环N可供選擇的方法，DS1820也可以用外部5V電源供電。與DS1820 的通信經(jīng)過(guò)一個(gè)單線接口。在單線接口情

59、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；</p><p>　　1）Read ROM(讀ROM)； </p><p>　　2)Match ROM(符合ROM)；</p><p>　　3)Search ROM(搜索ROM)；</p><p>　　4)Skip ROM(跳過(guò)ROM)；<

60、/p><p>　　5）Alarm Search(告警搜索)；</p><p>　　這些命令對(duì)每一器件的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，可使用存貯器和控制操作，然后主機(jī)可以提供六種存貯器和控制操作命令之一。</p><p>　　一個(gè)控制操作命

61、令指示DS1820 完成溫度測(cè)量。該測(cè)量的結(jié)果將放入DS1820 的高速暫存（便箋式）存貯器（Scratchpad memory），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。每一溫度告警觸發(fā)器TH和TL構(gòu)成一個(gè)字節(jié)的EEPROM。如果不對(duì)DS1820 施加告警搜索命令，這些寄存器可用作通用用戶存儲(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)。所有數(shù)據(jù)均以最低有效位在前的方式被讀寫。</p>

62、<p><b>　　寄生電源</b></p><p>　　方框圖(圖1)示出寄生電源電路。當(dāng)I/O或VDD 引腳為高電平時(shí)，這個(gè)電路便“取”得電源。只要符合指定的定時(shí)和電壓要求，I/O將提供足夠的功率（標(biāo)題為“單總線系統(tǒng)”一節(jié)）。寄生電源的優(yōu)點(diǎn)是雙重的：</p><p>　　1）利用此引腳，遠(yuǎn)程溫度檢測(cè)無(wú)需本地電源；</p><p>

63、　　2）缺少正常電源條件下也可以讀ROM；</p><p>　　為了使DS1820能完成準(zhǔn)確的溫度變換，當(dāng)溫度變換發(fā)生時(shí)，I/O 線上必須提供足夠的功率。因?yàn)镈S1820 的工作電流高達(dá)1mA ，5K 的上拉電阻將使I/O 線沒(méi)有足夠的驅(qū)動(dòng)能力。如果幾個(gè)SD1820 在同一條I/O 線上而且同時(shí)變換，那么這一問(wèn)題將變得特別尖銳。</p><p>　　有兩種方法確保DS1820 在其有效變換

64、期內(nèi)得到足夠的電源電流。第一種方法是發(fā)生溫度變換時(shí)，在I/O 線上提供一強(qiáng)的上拉。如圖2所示，通過(guò)使用一個(gè)MOSFET 把I/O 線直接拉到電源可達(dá)到這一點(diǎn)。當(dāng)使用寄生電源方式時(shí)VDD 引腳必須連接到地。</p><p>　　向DS1820 供電的另外一種方法是通過(guò)使用連接到VDD 引腳的外部電源，如圖3 所示這種方法的優(yōu)點(diǎn)是在I/O 線上不要求強(qiáng)的上拉。總線上主機(jī)不需向上連接便在溫度變換期間使線保持高電平。這就

65、允許在變換時(shí)間內(nèi)其它數(shù)據(jù)在單線上傳送。此外，在單線總線上可以放置任何數(shù)目的DS1820 ，而且如果它們都使用外部電源，那么通過(guò)發(fā)出跳過(guò)（Skip） ROM 命令和接著發(fā)出變換（Convert） T 命令，可以同時(shí)完成溫度變換。注意只要外部電源處于工作狀態(tài)，GND（地引）腳不可懸空。</p><p>　　在總線上主機(jī)不知道總線上DS1820 是寄生電源供電還是外部VDD 供電的情況下，在DS1820 內(nèi)采取了措施來(lái)

66、通知采用的供電方案。總線上主機(jī)通過(guò)發(fā)出跳過(guò)（Skip）ROM 的操作約定，然后發(fā)出讀電源命令，可以決定是否有需要強(qiáng)上拉的DS1820 在總線上。在此命令發(fā)出后，主機(jī)接著發(fā)出讀時(shí)間片。如果是寄生供電，DS1820 將在單線總線上送回“0”；如果由VDD 引腳供電，它將送回1。如果主機(jī)接收到一個(gè)“0”，它知道它必須在溫度變換期間在I/O 線上供一個(gè)強(qiáng)的上拉。有關(guān)此命令約定的詳細(xì)說(shuō)明見(jiàn)存貯器命令功能一節(jié)。</p><p&g

67、t;<b>　　運(yùn)用——測(cè)量溫度</b></p><p>　　SDS1820 通過(guò)使用在板（on-board）溫度測(cè)量專利技術(shù)來(lái)測(cè)量溫度。溫度測(cè)量電路的方框圖見(jiàn)圖4 所示。</p><p>　　DS1820 通過(guò)門開通期間內(nèi)低溫度系數(shù)振蕩器經(jīng)歷的時(shí)鐘周期個(gè)數(shù)計(jì)數(shù)來(lái)測(cè)量溫度，如果在門開通期結(jié)束前計(jì)數(shù)器達(dá)到零，那么溫度寄存器—它也被予置到-55℃的數(shù)值—將增量，指示溫度高

68、于-55℃。</p><p>　　同時(shí)，計(jì)數(shù)器用鈄率累加器電路所決定的值進(jìn)行予置。為了對(duì)遵循拋物線規(guī)律的振蕩器溫度特性進(jìn)行補(bǔ)償，這種電路是必需的。時(shí)鐘再次使計(jì)數(shù)器計(jì)值至它達(dá)到零。如果門開通時(shí)間仍未結(jié)束，那么此過(guò)程再次重復(fù)。</p><p>　　鈄率累加器用于補(bǔ)償振蕩器溫度特性的非線性，以產(chǎn)生高分辯率的溫度測(cè)量。通過(guò)改變溫度每升高一度，計(jì)數(shù)器必須經(jīng)歷的計(jì)數(shù)個(gè)數(shù)來(lái)實(shí)行補(bǔ)償。因此，為了獲得所需的

69、分辯率，計(jì)數(shù)器的數(shù)值以及在給定溫度處每一攝氏度的計(jì)數(shù)個(gè)數(shù)（鈄率累加器的值）二者都必須知道。</p><p>　　此計(jì)算在DS1820 內(nèi)部完成以提供0.5℃的分辯率。溫度讀數(shù)以16位、符號(hào)擴(kuò)展的二進(jìn)制補(bǔ)碼讀數(shù)形式提供表1 說(shuō)明輸出數(shù)據(jù)對(duì)測(cè)量溫度的關(guān)系。數(shù)據(jù)在單線接口上串行發(fā)送。DS1820 可以以0.5℃ 的增量值，在0.5℃至+125℃的范圍內(nèi)測(cè)量溫度。對(duì)于應(yīng)用華氏溫度的場(chǎng)合必須使用查找表或變換系數(shù)。</

70、p><p>　　注意在DS1820 中溫度是以1/2 LSB 最低有效位形式表示時(shí)產(chǎn)生以下9 位格式：</p><p>　　最高有效（符號(hào)）位被復(fù)制到存儲(chǔ)器內(nèi)兩字節(jié)的溫度寄存器中較高M(jìn)SB 的所有位，這種“符號(hào)擴(kuò)展”產(chǎn)生了如表1 所示的16 位溫度讀數(shù)。</p><p>　　以下的過(guò)程可以獲得較高的分辯率。首先，讀溫度，并從讀得的值截去0.5℃位(最低有效位)。這個(gè)值便

71、是TEMP_READ。然后可以讀留在計(jì)數(shù)器內(nèi)的值。此值是門開通期停止之后計(jì)數(shù)剩余</p><p>　?。–OUNT_REMAIN）。所需的最后一個(gè)數(shù)值是在該溫度處每一攝氏度的計(jì)數(shù)個(gè)數(shù)（COUNT_PER_C）。于是，用戶可以使用下式計(jì)算實(shí)際溫度：</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

72、一點(diǎn)是重要的，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)連接到單線總線上的器件必須具有漏極開路或三態(tài)輸出。DS1820 的單線接口（I/O 引腳是漏極開路的，其內(nèi)部等效電路如圖9 所示）多站multidrop 總線由單線總線和多個(gè)與之相連的從屬器件組成。單線總線要求近似等于5k的上拉電阻。</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)

73、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480us，那么總線上所有器件均被復(fù)位。</p><p>　　存在脈沖（presence pulse）使總線主機(jī)知道DS1820 在總線上并已準(zhǔn)備好工作。詳情見(jiàn)“單線信號(hào)”一節(jié)。</p><p><b>　　處理順序</b></p><p>　　經(jīng)過(guò)單線接口訪問(wèn)DS1820

74、 的協(xié)議（protocol）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><p><b>　　·處理/

75、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>　　2.8.2.2 ROM 操作命令</p><p>　　一旦總線主機(jī)檢測(cè)到從屬器件的存在，它便可以發(fā)出器件

76、ROM 操作命令之一。所有ROM 操作命令均為8 位長(zhǎng)，這些命令列表如下（參見(jiàn)圖6 的流程圖）。</p><p>　　·Read ROM(讀ROM) [33h]</p><p>　　此命令允許總線主機(jī)讀DS1820 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)DS1820 的情況下可以使用。如果總線上存在多于一個(gè)的從屬器件，那么當(dāng)所有

77、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（漏極開路會(huì)產(chǎn)生“線與”的結(jié)果）。</p><p>　　·Match ROM(“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)總線上特定的DS1820尋址。只有與64 位ROM 序列嚴(yán)格相符的DS1820 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

78、符的從片將等待復(fù)位脈沖。此命令在總線上有單個(gè)或多個(gè)器件的情況下均可使用</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)的從屬器件而且在Skip 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（漏極開路