【正文】 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。 the data must be transmitted to the DS18B20 starting with the least significant bit of byte 2. To verify data integrity, the scratchpad can be read (using the Read Scratchpad [BEh] mand) after the data is written. When reading the scratchpad, data is transferred over the 1Wire bus starting with the least significant 外文翻譯（原文） 6 bit of byte 0. To transfer the TH, TL and configuration data from the scratchpad to EEPROM, the master must issue the Copy Scratchpad [48h] mand. Byte0 Temperature LSB Byte1 Temperature MSB Byte2 TH Register for high temperature Byte3 TL Register for low temperature Byte4 Configuration Register Byte5 Reserved（ FFH） Byte6 Reserved（ OCH） Byte7 Reserved（ IOH） Byte8 Cyclic Redundancy Checks（ CRC） Figure Memory Map REGISTER Byte 4 of the scratchpad memory contains the configuration register, which is anized as illustrated in Figure 5. The user can set the conversion resolution of the DS18B20 using the R0 and R1 bits in this register as shown in Table 2. The powerup default of these bits is R0 = 1 and R1 = 1 (12bit resolution). Note that there is a direct tradeoff between resolution and conversion time. Bit 7 and bits 0 to 4 in the configuration register are reserved for internal use by the device and cannot be overwritten. BIT7 BIT6 BIT5 BIT4 BIT3 BIT2 BIT1 BIT0 TM R1 R0 1 1 1 1 1 Figure Register R0 R1 RESOLUTION(BITS) MAX CONVERSION TIME 外文翻譯（原文） 7 Table Resolution Configuration BUS SYSTEM The 1Wire bus system uses a single bus master to control one or more slave devices. The DS18B20 is always a slave. When there is only one slave on the bus, the system is referred to as a ―singledrop‖ system。C, respectively. The default resolution at powerup is 12bit. The DS18B20 powers up in a lowpower idle state. To initiate a temperature measurement and AtoD conversion, the master must issue a Convert T [44h] mand. Following the conversion, the resulting thermal data is stored in the 2byte temperature register in the scratchpad memory and the DS18B20 returns to its idle state. If the DS18B20 is powered by an external supply, the master can issue ―read time slots‖ (see the 1Wire Bus System section) after the Convert T mand and the DS18B20 will respond by transmitting 0 while 外文翻譯（原文） 4 the temperature conversion is in progress and 1 when the conversion is done. If the DS18B20 is powered with parasite power, this notification technique cannot be used since the bus must be pulled high by a strong pull up during the entire temperature conversion. The DS18B20 output temperature data is calibrated in degrees Celsius。C, 176。C ? Thermometer Resolution is User Selectable from 9 to 12 Bits ? Converts Temperature to 12Bit Digital Word in 750ms (Max) ? UserDefinable Nonvolatile (NV) Alarm Settings ? Alarm Search Command Identifies and Addresses Devices Whose Temperature is Outside Programmed Limits ? Software Compatible with the DS1822 ? Applications Include Thermostatic Controls, Industrial Systems, Consumer Products, Thermometers, or Any Thermally Sensitive System Figure 1 shows a block diagram of the DS18B20, and pin descriptions are given in the Pin Description table. The 64bit ROM stores the device’s unique serial code. The scratchpad memory contains the 2byte temperature register that stores the digital 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.