【正文】 this mand is issued the master must enable a 外文翻譯（原文） 11 strong pullup on the 1Wire bus. E2 [B8h] This mand recalls the alarm trigger values (TH and TL) and configuration data from EEPROM and places the data in bytes 2, 3, and 4, respectively, in the scratchpad memory. The master device can issue read time slots following the Recall E2mand and the DS18B20 will indicate the status of the recall by transmitting 0 while the recall is in progress and 1 when the recall is done. The recall operation happens automatically at powerup, so valid data is available in the scratchpad as soon as power is applied to the device. 6． READ POWER SUPPLY [B4h] The master device issues this mand followed by a read time slot to determine if any DS18B20s on the bus are using parasite power. During the read time slot, parasite powered DS18B20s will pull the bus low, and externally powered DS18B20s will let the bus remain high. SIGNALING The DS18B20 uses a strict 1Wire munication protocol to ensure data integrity. Several signal types are defined by this protocol: reset pulse, presence pulse, write 0, write 1, read 0, and read 1. The bus master initiates all these signals, with the exception of the presence pulse. （ 1） INITIALIZATION PROCEDURE—RESET AND PRESENCE PULSES All munication with the DS18B20 begins with an initialization sequence that consists of a reset pulse from the master followed by a presence pulse from the DS18B20. This is illustrated in Figure 6. When the DS18B20 sends the presence pulse in response to the reset, it is indicating to the master that it is on the bus and ready to operate. During the initialization sequence the bus master transmits (TX) the reset pulse by pulling the 1Wire bus low for a minimum of 480181。C, 176。C (67176。C and is accurate to 177。C to +85176。176。 for Fahrenheit applications, a lookup table or conversion routine must be used. The temperature data is stored as a 16bit signextended two’s plement 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 DS18B20 is configured for 12bit resolution, all bits in the temperature register will contain valid data. For 11bit resolution, bit 0 is undefined. For 10bit resolution, bits 1 and 0 are undefined, and for 9bit resolution bits 2, 1, and 0 are undefined. Table 1 gives examples of digital output data and the corresponding temperature reading for 12bit resolution conversions. bit7 bit6 bit5 bit4 bit3 bit2 bit1 bit0 LS Byte 23 22 21 20 21 22 23 24 bit15 bit14 bit13 bit12 bit11 bit10 bit9 bit8 MS Byte S S S S S 26 25 24 Figure Register Format TEMPERATURE DIGITAL OUTPUT (BINARY) DIGITAL OUTPUT (HEX) +125℃ 0000 0111 1101 0000 07D0H +℃ 0000 0001 1001 0001 0191H 0℃ 0000 0000 0000 0000 0000H ℃ 1111 1110 0110 1111 FE6FH 55℃ 1111 1100 1001 0000 FC90H Table LASERED ROM CODE 外文翻譯（原文） 5 Each DS18B20 contains a unique 64–bit code (see Figure 3) stored in ROM. The least significant 8 bits of the ROM code contain the DS18B20’s 1Wire 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. The 64bit ROM code and associated ROM function control logic allow the DS18B20 to operate as a 1Wire device using the protocol detailed in the 1Wire Bus System section. 8BIT CRC 48BIT SERIAL NUMBER 8BIT FAMILY CODE MSB LSB MSB LSB MSB Figure Lasered ROM Code The DS18B20’s memory is anized as shown in Figure 4. The memory consists of an SRAM scratchpad with nonvolatile EEPROM storage for the hi gh and low alarm trigger registers (TH and TL) and configuration register. Note that if the DS18B20 alarm function is not used, the TH and TL registers can serve as generalpurpose memory. Byte 0 and byte 1 of the scratchpad contain the LSB and the MSB of the temperature register, respectively. These bytes are readonly. Bytes 2 and 3 provide access to TH and TL registers. Byte 4 contains the configuration register data. Bytes 5, 6, and 7 are reserved for internal use by the device and cannot be overwritten. Byte 8 of the scratchpad is readonly and contains the CRC code for bytes 0 through 7 of the scratchpad. The DS18B20 generates this CRC using the method described in the CRC Generation section. Data is written to bytes 2, 3, and 4 of the scratchpad using the Write Scratchpad [4Eh] mand。s and then transmits a presence pulse by pulling the 1Wire bus low for 60181。s recovery time between individual write slots. Both types of write time slots are initiated by the master pulling the 1Wire bus low (see Figure 7). To generate a Write 1 time slot, after pulling the 1Wire bus low, the bus master must release the 1Wirebus within 15181。s after the falling edge that initiated the read time slot. Therefore, the master must release the bus and then sample the bus state within 15181。另外， DS18B20 能夠從數(shù)據(jù)線中直接獲得能量（寄生電源），消除了對外部供電的需求。F） ? 10176。配置寄存器允許用戶設(shè)定 9 位、 10 位、 11 位和 12 位的溫度分辨率。當(dāng)總線高電平時(shí)能量由單線上拉電阻經(jīng)過 DQ 引腳獲得。C, 和176。 DS18B20 輸出溫度數(shù)據(jù)是攝氏度標(biāo)準(zhǔn)，若要轉(zhuǎn)為華氏溫度，必須使用查表或轉(zhuǎn)換子程序。接著 48 位包含一個(gè)唯一的序列號。字節(jié) 2 和字節(jié) 3 提供提供 TH 和 TL寄存器的接口。 Byte0 溫度測量值低 8 位 LSB Byte1 溫度測量值高 8 位 MSB Byte2 TH 高溫寄存器 外文翻譯（譯文） 20 Byte3 TL 低溫寄存器 Byte4 配置寄存器 Byte5 預(yù)留（ FFH） Byte6 預(yù)留（ OCH） Byte7 預(yù)留（ IOH） Byte8 循環(huán)冗余碼校驗(yàn)（ CRC） 圖 存儲(chǔ)器映射 高速暫存存儲(chǔ)器的字節(jié) 4 包含配置寄存器，正如 圖 5 中 那樣定義。所有數(shù)據(jù)和命令通過單總線首先傳輸最低有效位。 （ 2） ROM 命令 在總線主機(jī)檢測到一 個(gè)應(yīng)答脈沖后，就可以發(fā)出一個(gè) ROM 命令。如果總線上只有一個(gè)從機(jī)，那么更為簡單的讀 ROM 命令可以代替搜索命令來處理。 如此看來，允許主機(jī)讀取從機(jī)而不需要發(fā)送設(shè)備的64 位 ROM 碼，這樣可以節(jié)省操作時(shí)間。如果設(shè)備采用寄生電源，此命令發(fā)出之后最多在 10181。開始字節(jié)的數(shù)據(jù)被寫入 TH 寄存器（暫存器的字節(jié) 2），第二