【正文】 gital output from the temperature sensor. In addition, the scratchpad provides access to the 1byte upper and lower alarm trigger registers (TH and TL) and the 1byte configuration register. The configuration register allows the user to set the resolution of the temperature todigital conversion to 9, 10, 11, or 12 bits. The TH, TL, and configuration registers are nonvolatile (EEPROM), so they will retain data when the device is powered down. The DS18B20 uses Maxim’s exclusive 1Wire bus protocol that implements bus munication using one control signal. The control line requires a weak pull up resistor since all devices are linked to the bus via a 3state or opendrain port (the DQ pin in the case of the DS18B20). In this bus system, the microprocessor (the master device) identifies and addresses devices on the bus using each device’s unique 64bit code. Because each device has a unique code, the number of devices that can be addressed on one DS18B20 bus is virtually unlimited. The 1Wire bus protocol, 外文翻譯（原文） 3 including detailed explanations of the mands and “ time slots,‖ is covered in the 1Wire Bus System section. Another feature of the DS18B20 is the ability to operate without an external power supply. Power is instead supplied through the 1Wire pull up resistor via the DQ pin when the bus 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 1Wire bus is referred to as ―parasite power.‖ As an alternative, the DS18B20 may also be powered by an external supply on VDD. 6 4 B I T R O MA N D1 W I R E P O R TM E M O R Y C O N T R O LL O G I CS C R A T C H P A D T E M P E R A T U R E S E N S O R A L A R M H I G H T R I G G E R ( T H ) A L A R M L O W T R I G G E R ( T L ) C O N F I G U R A T I O N R E G I S T E R 8 B I T C R C G E N E R A T O R P O W E R S U P P L Y S E N S E I N T E R N A L V d dP A R A S I T E P O W E R C I R C U I T C p pV p u4 . 7 KD QG N DV d d Figure Block Diagram —MEASURING TEMPERATUR The core functionality of the DS18B20 is its directtodigital temperature sensor. The resolution of the temperature sensor is userconfigurable to 9, 10, 11, or 12 bits, corresponding to increments of 176。 all other slaves on the bus will wait for a reset pulse. ROM [CCh] The master can use this mand to address all devices on the bus simultaneously without sending out any ROM code information. For example, the master can make all DS18B20s on the bus perform simultaneous temperature conversions by issuing a Skip ROM mand followed by a Convert T [44h] mand. Note that the Read Scratchpad [BEh] mand can follow the Skip ROM mand only if there is a single slave device on the bus. In this case, time is saved by allowing the master to read from the slave without sending the device’s 64bit ROM code. A Skip ROM mand followed by a Read Scratchpad mand will cause a data collision on the bus if there is more than one slave since multiple devices will attempt to transmit data simultaneously. SEARCH [ECh] The operation of this mand is identical to the operation of the Search ROM mand except that only slaves with a set alarm flag will respond. This mand allows the master device to determine if any DS18B20s experienced an alarm condition during the most recent temperature conversion. After every Alarm Search cycle (., Alarm Search mand followed by data exchange), the bus master must return to Step 1 (Initialization) in the transaction sequence. （ 3） DS18B20 FUNCTION COMMANDS After the bus master has used a ROM mand to address the DS18B20 with which it wishes to municate, the master can issue one of the DS18B20 function mands. These mands allow the master to write to and read from the DS18B20’s scratchpad memory, initiate temperature conversions and determine the power supply mode. 外文翻譯（原文） 10 T [44h] This mand initiates a single temperature conversion. Following the conversion, the resulting thermal data is stored in the 2byte temperature register in the scratchpad memory and the DS18B20 returns to its lowpower idle state. If the device is being used in parasite power mode, within 10181。 s m i n i m u mD S 1 8 B 2 0 w a i t s1 5 ~ 6 0 181。s to 60181。它的工作溫度范圍為 55176。包括高壓交流電環(huán)境控制、內置溫度檢測系統(tǒng)建筑，或者機器、處理器和控制系統(tǒng)在內的應用程序都會從這個特點中受益。176?？刂凭€需要一個較小的上拉電阻，因為所有的設備通過一個三態(tài)漏極開路端口（如 DS18B20 的 DQ 引腳）連在總線上。另外一種選擇是 DS18B20 由接在 VDD 的外部電源供電。 DS18B20 上電后處于空閑狀態(tài)。如果 DS18B20被設定為 12 位分辨率，溫度寄存器中的所有位均為有效數據 ；對 11 位分辨率，位 0 無定義。 8 位 CRC 編號 48 位序列號 8 位產品系列編碼 圖 位激光 ROM 碼 DS18B20 的存儲器如同圖 4 中那樣被組織。 DS18B20使用 CRC 產生一節(jié)中的方法形成這個 CRC 碼。在分辨率和轉換時間之間有個直接的折衷。此規(guī)則的例外就是是搜索命令和告警搜索命令。共有五種 ROM 命令，每一個命令均是 8 位長。若所有從機同時試圖響應主機信號外文翻譯（譯文） 22 時就會發(fā)生數據沖突。這個命令使主機能夠確定 DS18B20 在最近的溫度轉換時是否處于告警狀態(tài)。寄生電源方式下這種傳遞方式不能使用，因為總線電平在轉換期外文翻譯（譯文） 23 間被拉高。數據傳輸開始于字節(jié) 0 的最低有效位，通過 暫存器持續(xù)讀取直到第九個字節(jié)（字節(jié) 8循環(huán)冗余校驗碼）被讀取。 （ 3） DS18B20 功能命令 在總線主機使用 ROM 命令尋址所希望進行通信的 DS18B20 后，主機必須發(fā)出 DS18B20 的一個功能命令。 ROM 命令 CCH 主機能采用此命令同時訪問總線上所有設備，無需發(fā)出任何 ROM 碼。 ROM 命令操作流程表在圖中給出。 （ 1）初始化 單總線上的所有數據交換都開始于初始化序列。 位 7 位 6 位 5 位 4 位 3 位 2 位 1 位 0 TM R1 R0 1 1 1 1 1 圖 R0 R1 分辨率 溫度最大轉換時間（ ms） 0 0 1 1 0 1 0 1 9 位 10 位 11 位 12 位 375 750 表 一線總線系統(tǒng)使用單總線主控來控制一個或多個從機設備。為了檢驗數據完整性，在數據被寫入之后可以讀取暫存器（使用讀暫存器命令）。如果 DS18B20 不使用告警功能，那么 TH、 TL 和配置寄存器就作為通用寄存器使用。表 1 給出了數字輸出數據和相應的 12 位分辨率溫度讀取轉換。轉換命令后，采集的溫度數據存儲在暫存器的 2 字節(jié)的溫度寄存器中，然后 DS18B20恢復到空閑狀態(tài)。溫度傳感器的分辨率是用戶可配置的 9 位、 10 位、 11 位或 12 位，分別對應的增量為 176。因為每個設備 有唯一的序列碼，因此能夠被同一個 DS18B20 尋址的設備數量幾乎無限的。64 位 ROM 存儲了設備的獨有的序列號。C 到 +12176。C ，且在 10 到 85 范圍內的精度為 177。s in duration with a minimum of a 1181。 sM a s t e r R x4 8 0 181。s (max) after