参数资料
型号: DS18B20Z/T&R
厂商: Maxim Integrated
文件页数: 10/22页
文件大小: 528K
描述: IC THERM MICROLAN PROG-RES 8SOIC
产品培训模块: Lead (SnPb) Finish for COTS
Obsolescence Mitigation Program
标准包装: 2,500
功能: 温度计,恒温计
传感器类型: 内部
感应温度: -55°C ~ 125°C
精确度: ±2°C(最小值)
拓扑: 寄存器库,变签式暂存器
输出类型: 1-Wire?
输出警报:
输出风扇:
电源电压: 3 V ~ 5.5 V
工作温度: -55°C ~ 125°C
安装类型: 表面贴装
封装/外壳: 8-SOIC(0.154",3.90mm 宽)
供应商设备封装: 8-SOIC
包装: 带卷 (TR)
DS18B20
 
10 of 22 
TRANSACTION SEQUENCE
The transaction sequence for accessing the DS18B20 is as follows:
Step 1. Initialization
Step 2. ROM Command (followed by any required data exchange)
Step 3. DS18B20 Function Command (followed by any required data exchange)
It is very important to follow this sequence every time the DS18B20 is accessed, as the DS18B20 will not
respond if any steps in the sequence are missing or out of order. Exceptions to this rule are the Search
ROM [F0h] and Alarm Search [ECh] commands. After issuing either of these ROM commands, the
master must return to Step 1 in the sequence.
 
INITIALIZATION
All transactions on the 1-Wire bus begin with an initialization sequence. The initialization sequence
consists of a reset pulse transmitted by the bus master followed by presence pulse(s) transmitted by the
slave(s). The presence pulse lets the bus master know that slave devices (such as the DS18B20) are on the
bus and are ready to operate. Timing for the reset and presence pulses is detailed in the 1-Wire Signaling
section.
 
ROM COMMANDS
After the bus master has detected a presence pulse, it can issue a ROM command. These commands
operate on the unique 64-bit ROM codes of each slave device and allow the master to single out a specific
device if many are present on the 1-Wire bus. These commands also allow the master to determine how
many and what types of devices are present on the bus or if any device has experienced an alarm
condition. There are five ROM commands, and each command is 8 bits long. The master device must
issue an appropriate ROM command before issuing a DS18B20 function command. A flowchart for
operation of the ROM commands is shown in Figure 11.
SEARCH ROM [F0h]
When a system is initially powered up, the master must identify the ROM codes of all slave devices on
the bus, which allows the master to determine the number of slaves and their device types. The master
learns the ROM codes through a process of elimination that requires the master to perform a Search ROM
cycle (i.e., Search ROM command followed by data exchange) as many times as necessary to identify all
of the slave devices. If there is only one slave on the bus, the simpler Read ROM command (see below)
can be used in place of the Search ROM process. For a detailed explanation of the Search ROM
procedure, refer to the  i
Button
?/DIV>
  Book of Standards at  www.maxim-ic.com/ibuttonbook
. After every
Search ROM cycle, the bus master must return to Step 1 (Initialization) in the transaction sequence.
READ ROM [33h]
This command can only be used when there is one slave on the bus. It allows the bus master to read the
slaves 64-bit ROM code without using the Search ROM procedure. If this command is used when there
is more than one slave present on the bus, a data collision will occur when all the slaves attempt to
respond at the same time.  
MATCH ROM [55h]
The match ROM command followed by a 64-bit ROM code sequence allows the bus master to address a
specific slave device on a multidrop or single-drop bus. Only the slave that exactly matches the 64-bit
ROM code sequence will respond to the function command issued by the master; all other slaves on the
bus will wait for a reset pulse.
i
Button is a registered trademark of Maxim Integrated Products, Inc.
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