温度传感器DS18b20接口设计(4课时).ppt

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1、89s52与温度传感器DS18b20接口设计DS18b20 FEATURES1、Unique 1-WireTM interface requires only one port pin for communication2、Measures temperatures from-55C to+125C；Fahrenheit equivalent is-67F to+257F 3、0.5 C accuracy from-10C to+85C4、Thermometer resolution is programmable from 9 to 12 bits5、Converts 12-bit temp

2、erature to digital word in 750 ms(max.)DS18b20 简介1、单总线技术，只需要一个端口与主机通信2、温度测量范围摄氏-55C+125C，华氏-67F +257F 3、-10C +85C间测量误差在 0.5 C 以内4、温度测量精度可编程控制（9位到12位）5、12位精度时温度转换时间750ms（最大）DS18B20 MEMORY MAPDS18B20 CONFIGURATION REGISTERBits 0-4 are dont cares on a write but will always read out“1”.Bit 7 is dont car

3、e on a write but will always read out“0”.R0,R1:Thermometer resolution bits.Table below defines the resolution of the digital thermometer,based on the settings of these two bits.There is a direct tradeoff between resolution and conversion time,as depicted in the AC Electrical Characteristics.The fact

4、ory default of these EEPROM bits is R0=1 andR1=1(12-bit conversions).DS18B20 与单片机通信流程单片机与DS18B20一次完整的通信过程由以下4步组成：所有操作都必须由初始化脉冲开始，波形如图，单片机先输出一个480960us低电平到DQ引脚，再将DQ引脚置高电平，过1560us后检测DQ引脚状态，若为低电平则DS18B20工作正常，否则初始化失败，不能正常测量温度。DS18B20 初始化DS18B20 ROM操作命令1、Read ROM 33H2、Match ROM 55H3、Skip ROM CCH4、Search

5、ROM F0H5、Alarm Search ECHDS18B20 内存操作命令1、Write Scratchpad 4EHThis command writes to the scratchpad of the DS18B20,starting at the TH register.The next three bytes written will be saved in scratchpad memory at address locations 2 through 4.All three bytes must be written before a reset is issued.1、写暂

6、存器命令【4EH】这个命令为由TH寄存器开始向DS18B20暂存器写入数据，4EH命令后的3字节数据将被保存到暂存器的地址2、3、4（TH、TL、CONFIG）三个字节。所有数据必须在复位脉冲前写完。即如果只想写一个字节的数据到地址2，可按如下流程：1、初始化 2、写0CCH 跳过ROM检测 3、写4EH 4、写1字节数据 5、复位 即向DQ输出480960us低电平2、Read Scratchpad BEHThis command reads the contents of the scratchpad.Reading will commence at byte 0 and will con

7、tinue through the scratchpad until the 9th(byte 8,CRC)byte is read.If not all locations are to be read,the master may issue a reset to terminate reading at any time.2、读暂存命令【BEH】这个命令由字节0读取9个暂存器内容，如果不需要读取所有暂存内容，可随时输出复位脉冲终止读取过程DS18B20 内存操作命令DS18B20 内存操作命令3、Convert T 44HThis command begins a temperature

8、 conversion.No further data is required.The temperature conversion will be performed and then the DS18B20 will remain idle.If the bus master issues read time slots following this command,the DS18B20 will output 0 on the bus as long as it is busy making a temperature conversion;it will return a 1 whe

9、n the temperature conversion is complete.If parasite-powered,the bus master has to enable a strong pullup for a period greater than tconv immediately after issuing this command.3、转换温度命令【44H】这个命令启动温度转换过程。转换温度时DS18B20保持空闲状态，此时如果单片机发出读命令，DS18B20将输出0直到转换完成，转换完成后将输出1。主程序流程图设置DS18B20工作方式设为12位转换模式，即(CONFIG

10、)=01111111B。根据4步操作法设置流程图如下：输出转换温度命令读取温度数据思考：通过前面的学习我们了解了DS18B20的控制命令和数据传输过程，但这些命令都是一个字节的数据，那么怎么通过单总线发送这些命令以及通过单总线读取12位温度转换数据呢？只能是用串行的方式一位一位的传输，那么读写时序就非常重要了Write Time SlotsA write time slot is initiated when the host pulls the data line from a high logic level to a low logic level.There are two types

11、 of write time slots:Write 1 time slots and Write 0 time slots.All write time slots must be a minimum of 60s in duration with a minimum of a 1s recovery time between individual write cycles.The DS18B20 samples the DQ line in a window of 15s to 60s after the DQ line falls.If the line is high,a Write

12、1 occurs.If the line is low,a Write 0 occurs(see Figure 12).For the host to generate a Write 1 time slot,the data line must be pulled to a logic low level and then released,allowing the data line to pull up to a high level within 15s after the start of the write time slot.For the host to generate a

13、Write 0 time slot,the data line must be pulled to a logic low level and remain low for 60s.写时隙写时隙由DQ引脚的下降沿引起。18B20有写1和写0两种写时隙。所有写时隙必须持续至少60s，两个时隙之间至少有1s的恢复时间。DS18B20在DQ下降沿后15s60s间采样DQ引脚，若此时DQ为高电平，则写入一位1，若此时DQ为低电平，则写入一位0，如下图所示。所以，若想写入1，则单片机应先将DQ置低电平，15us后再将DQ置高电平，持续45s；若要写入0，则将DQ置低电平，持续60s。写流程图Read T

14、ime SlotsThe host generates read time slots when data is to be read from the DS18B20.A read time slot is initiated when the host pulls the data line from a logic high level to logic low level.The data line must remain at a low logic level for a minimum of 1s;output data from the DS18B20 is valid for

15、 15s after the falling edge of the read time slot.The host therefore must stop driving the DQ pin low in order to read its state 15s from the start of the read slot(see Figure 12).By the end of the read time slot,the DQ pin will pull back high via the external pullup resistor.All read time slots mus

16、t be a minimum of 60s in duration with a minimum of a 1s recovery time between individual read slots.Figure 12 shows that the sum of TINIT,TRC,and TSAMPLE must be less than 15s.Figure 14 shows that system timing margin is maximized by keeping TINIT and TRC as small as possible and by locating the ma

17、ster sample time towards the end of the 15s period.读时隙读时隙由DQ下降沿引起，持续至少1s的低电平后释放总线（DQ置1）DS18B20的输出数据将在下降沿15s后输出，此时单片机可读取1位数据。读时隙结束时要将DQ置1。所有读时隙必须持续至少60s，两个时隙之间至少有1s的恢复时间。图12表示TINIT、TRC和TSAMPLE之和必须小于15s，图14表示应尽可能的将TINIT和TRC保持最小而用TSAMPLE填充剩余时间读流程图实验五：基于DS18B20的温度传感器设计一、实验目的1、了解单总线器件的工作方式和编程原理。2、掌握DS18B20和单片机接口设计方法。二、实验内容利用单片机实验板设计温度测量程序，精确到0.1C发挥部分：1、超过设定温度范围报警（声、光、显示）2、温度控制（模拟）三、实验原理见课件