【正文】 master may then provide any one of the six memory and control function mands. One control function mand 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 read by issuing a memory function mand which reads the contents of the scratchpad memory. The temperature alarm triggers TH and TL consist of one byte EEPROM each. If the alarm search mand is not applied to the DS1820, these registers may be used as general purpose user memory. Writing TH and TL is done using a memory function mand. Read access to these registers is through the scratchpad. All data is read and written least significant bit block diagram (Figure 1) shows the parasite powered circuitry. This circuitry “steals” power whenever the I/O or VDD pins are high. I/O will provide sufficient power as long as the specified timing and voltage requirements are met (see the section titled “1–Wire Bus System”). The advantages of parasite power are two–fold: 1) by parasiting off this pin, no local power source is needed for remote sensing of temperature, 2) the ROM may be read in absence of normal power. In order for the DS1820 to be able to perform accurate temperature 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 drive 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. There are two ways to assure that the DS1820 has 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 acplished 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 to the E2 memory or initiates temperature conversions. When using the parasite power mode, the VDD pin must be tied to ground. Another method of supplying current to the DS1820 is through the use of an external power supply tied to the VDD pin, as shown in Figure 3. The advantage to this is that the strong pull–up is not required on the I/O line, and the bus master need not be tied up holding that line high during temperature conversions. This allows other data traffic on the 1–Wire bus during the conversion time. In addition, any number of DS1820’s may be placed on the 1–Wire bus, and if they all use external power, they may all simultaneously perform temperature conversions by issuing the Skip ROM mand and then issuing the Convert T mand. Note that as long as the external power supply is active, the GND pin may not be floating. The use of parasite power is not remended above 100176。C in 176?？捎脭?shù)據(jù)線供電； 應用范圍包括恒溫控制，工業(yè)系統(tǒng)，消費類產(chǎn)品，溫度計或任何熱敏系統(tǒng)。 一個控制操作命令指示 DS1820 完成溫度測量。寄生電源的優(yōu)點是雙重的： 1）利用此引腳，遠程溫度檢測無需本地電源； 2）缺少正常電源條件下也可以讀 ROM； 為了使 DS1820能完成準確的溫度變換，當溫度變換發(fā)生時， I/O 線上必須提供足夠的功率。總線上主機不需向上連接便在溫度變換期間使線保持高電平。如果主機接收到一個“ 0”，它知道它必須在溫度變換期間在 I/O 線上供一個強的上拉。如果門開通時間仍未結(jié)束，那么此過程再次重復。對于應用華氏溫度的場合必須使用查找表或變換系數(shù)。于是，用戶可以使用下式計算實際溫度： 硬件接法 根據(jù)定義，單線總線只有一根線：這一點是重要的，即線上的第一個器件能在適當?shù)臅r間驅(qū)動該總線。詳情見“單線信號”一節(jié)。所有 ROM 操作命令均為 8 位長，這些命令列表如下（參見圖 6 的流程圖）。只有與 64 位 ROM 序列嚴格相符的 DS1820 才能對后繼的存貯器操作命令作出響應。 。此命令在總線上有單個或多個器件的情況下