資源簡介
DS18B20是單總線數(shù)字傳感器，共有6種信號(hào)類型：復(fù)位脈沖、應(yīng)答脈沖、寫0、寫1、讀0和讀1。所有這些信號(hào)，除了應(yīng)答脈沖以外，都由主機(jī)發(fā)出同步信號(hào)。并且發(fā)送所有的命令和數(shù)據(jù)都是字節(jié)的低位在前。
這幾個(gè)信號(hào)的時(shí)序如下：
1）復(fù)位脈沖和應(yīng)答脈沖
單總線上的所有通信都是以初始化序列開始。主機(jī)輸出低電平，保持低電平時(shí)間至少480us，以產(chǎn)生復(fù)位脈沖。接著主機(jī)釋放總線，4.7K的上拉電阻將單總線拉高，延時(shí)15～60us，并進(jìn)入接收模式(Rx)。接著DS18B20拉低總線60~240us，以產(chǎn)生低電平應(yīng)答脈沖，若為低電平，再延時(shí)480us。
2）寫時(shí)序
寫時(shí)序包括寫0時(shí)序和寫1時(shí)序。所有寫時(shí)序至少需要60us，且在2次獨(dú)立的寫時(shí)序之間至少需要1us的恢復(fù)時(shí)間，兩種寫時(shí)序均起始于主機(jī)拉低總線。寫1時(shí)序：主機(jī)輸出低電平，延時(shí)2us，然后釋放總線，延時(shí)60us。寫0時(shí)序：主機(jī)輸出低電平，延時(shí)60us，然后釋放總線，延時(shí)2us。
3）讀時(shí)序
單總線器件僅在主機(jī)發(fā)出讀時(shí)序時(shí)，才向主機(jī)傳輸數(shù)據(jù)，所以，在主機(jī)發(fā)出讀數(shù)據(jù)命令后，必須馬上產(chǎn)生讀時(shí)序，以便從機(jī)能夠傳輸數(shù)據(jù)。所有讀時(shí)序至少需要60us，且在2次獨(dú)立的讀時(shí)序之間至少需要1us的恢復(fù)時(shí)間。每個(gè)讀時(shí)序都由主機(jī)發(fā)起，至少拉低總線1us。主機(jī)在讀時(shí)序期間必須釋放總線，并且在時(shí)序起始后的15us之內(nèi)采樣總線狀態(tài)。典型的讀時(shí)序過程為：主機(jī)輸出低電平延時(shí)2us，然后主機(jī)轉(zhuǎn)入輸入模式延時(shí)12us，然后讀取單總線當(dāng)前的電平，然后延時(shí)50us。
DS18B20的溫度讀取過程一般為：復(fù)位->發(fā)SKIPROM命令（0XCC）->發(fā)開始轉(zhuǎn)換命令（0X44）->延時(shí)->復(fù)位->發(fā)送SKIPROM命令（0XCC）->發(fā)讀存儲(chǔ)器命令（0XBE）->連續(xù)讀出兩個(gè)字節(jié)數(shù)據(jù)(即溫度)->結(jié)束。
代碼片段和文件信息
/**
??******************************************************************************
??*?@file????system_stm32l0xx.c
??*?@author??MCD?Application?Team
??*?@version?V1.4.0
??*?@date????16-October-2015
??*?@brief???CMSIS?Cortex-M0+?Device?Peripheral?Access?layer?System?Source?File.
??*
??*???This?file?provides?two?functions?and?one?global?variable?to?be?called?from?
??*???user?application:
??*??????-?SystemInit（）:?This?function?is?called?at?startup?just?after?reset?and?
??*??????????????????????before?branch?to?main?program.?This?call?is?made?inside
??*??????????????????????the?“startup_stm32l0xx.s“?file.
??*
??*??????-?SystemCoreClock?variable:?Contains?the?core?clock?（HCLK）?it?can?be?used
??*??????????????????????????????????by?the?user?application?to?setup?the?SysTick?
??*??????????????????????????????????timer?or?configure?other?parameters.
??*?????????????????????????????????????
??*??????-?SystemCoreClockUpdate（）:?Updates?the?variable?SystemCoreClock?and?must
??*?????????????????????????????????be?called?whenever?the?core?clock?is?changed
??*?????????????????????????????????during?program?execution.
??*
??*
??******************************************************************************
??*?@attention
??*
??*?©?COPYRIGHT（c）?2015?STMicroelectronics
??*
??*?Redistribution?and?use?in?source?and?binary?forms?with?or?without?modification
??*?are?permitted?provided?that?the?following?conditions?are?met:
??*???1.?Redistributions?of?source?code?must?retain?the?above?copyright?notice
??*??????this?list?of?conditions?and?the?following?disclaimer.
??*???2.?Redistributions?in?binary?form?must?reproduce?the?above?copyright?notice
??*??????this?list?of?conditions?and?the?following?disclaimer?in?the?documentation
??*??????and/or?other?materials?provided?with?the?distribution.
??*???3.?Neither?the?name?of?STMicroelectronics?nor?the?names?of?its?contributors
??*??????may?be?used?to?endorse?or?promote?products?derived?from?this?software
??*??????without?specific?prior?written?permission.
??*
??*?THIS?SOFTWARE?IS?PROVIDED?BY?THE?COPYRIGHT?HOLDERS?AND?CONTRIBUTORS?“AS?IS“
??*?AND?ANY?EXPRESS?OR?IMPLIED?WARRANTIES?INCLUDING?BUT?NOT?LIMITED?TO?THE
??*?IMPLIED?WARRANTIES?OF?MERCHANTABILITY?AND?FITNESS?FOR?A?PARTICULAR?PURPOSE?ARE
??*?DISCLAIMED.?IN?NO?EVENT?SHALL?THE?COPYRIGHT?HOLDER?OR?CONTRIBUTORS?BE?LIABLE
??*?FOR?ANY?DIRECT?INDIRECT?INCIDENTAL?SPECIAL?EXEMPLARY?OR?CONSEQUENTIAL
??*?DAMAGES?（INCLUDING?BUT?NOT?LIMITED?TO?PROCUREMENT?OF?SUBSTITUTE?GOODS?OR
??*?SERVICES;?LOSS?OF?USE?DATA?OR?PROFITS;?OR?BUSINESS?INTERRUPTION）?HOWEVER
??*?CAUSED?AND?ON?ANY?THEORY?OF?LIABILITY?WHETHER?IN?CONTRACT?STRICT?LIABILITY
??*?OR?TORT?（INCLUDING?NEGLIGENCE?OR?OTHERWISE）?ARISING?IN?ANY?WAY?OUT?OF?THE?USE
??*?OF?THIS?SOFTWARE?EVEN?IF?ADVISED?OF?THE?POSSIBILITY?OF?SUCH?DAMAGE.
??*
??******************************************************************************
??*/
/**?@addtog ?屬性????????????大小?????日期????時(shí)間???名稱
-----------?---------??----------?-----??----
?????文件???????5189??2016-01-20?22:13??DS18B20_USART\STM32L053\.mxproject
?????文件?????252926??2015-12-15?15:15??DS18B20_USART\STM32L053\Drivers\CMSIS\Device\ST\STM32L0xx\Include\stm32l011xx.h
?????文件?????259183??2015-12-15?15:15??DS18B20_USART\STM32L053\Drivers\CMSIS\Device\ST\STM32L0xx\Include\stm32l021xx.h
?????文件?????256932??2015-12-15?15:15??DS18B20_USART\STM32L053\Drivers\CMSIS\Device\ST\STM32L0xx\Include\stm32l031xx.h
?????文件?????263189??2015-12-15?15:15??DS18B20_USART\STM32L053\Drivers\CMSIS\Device\ST\STM32L0xx\Include\stm32l041xx.h
?????文件?????265915??2015-12-15?15:15??DS18B20_USART\STM32L053\Drivers\CMSIS\Device\ST\STM32L0xx\Include\stm32l051xx.h
?????文件?????319600??2015-12-15?15:15??DS18B20_USART\STM32L053\Drivers\CMSIS\Device\ST\STM32L0xx\Include\stm32l052xx.h
?????文件?????326104??2015-12-15?15:15??DS18B20_USART\STM32L053\Drivers\CMSIS\Device\ST\STM32L0xx\Include\stm32l053xx.h
?????文件?????272172??2015-12-15?15:15??DS18B20_USART\STM32L053\Drivers\CMSIS\Device\ST\STM32L0xx\Include\stm32l061xx.h
?????文件?????325857??2015-12-15?15:15??DS18B20_USART\STM32L053\Drivers\CMSIS\Device\ST\STM32L0xx\Include\stm32l062xx.h
?????文件?????332361??2015-12-15?15:15??DS18B20_USART\STM32L053\Drivers\CMSIS\Device\ST\STM32L0xx\Include\stm32l063xx.h
?????文件?????277472??2015-12-15?15:15??DS18B20_USART\STM32L053\Drivers\CMSIS\Device\ST\STM32L0xx\Include\stm32l071xx.h
?????文件?????335861??2015-12-15?15:15??DS18B20_USART\STM32L053\Drivers\CMSIS\Device\ST\STM32L0xx\Include\stm32l072xx.h
?????文件?????342501??2015-12-15?15:15??DS18B20_USART\STM32L053\Drivers\CMSIS\Device\ST\STM32L0xx\Include\stm32l073xx.h
?????文件?????283729??2015-12-15?15:15??DS18B20_USART\STM32L053\Drivers\CMSIS\Device\ST\STM32L0xx\Include\stm32l081xx.h
?????文件?????342118??2015-12-15?15:15??DS18B20_USART\STM32L053\Drivers\CMSIS\Device\ST\STM32L0xx\Include\stm32l082xx.h
?????文件?????348758??2015-12-15?15:15??DS18B20_USART\STM32L053\Drivers\CMSIS\Device\ST\STM32L0xx\Include\stm32l083xx.h
?????文件???????8511??2015-12-15?15:15??DS18B20_USART\STM32L053\Drivers\CMSIS\Device\ST\STM32L0xx\Include\stm32l0xx.h
?????文件???????3842??2015-12-15?15:15??DS18B20_USART\STM32L053\Drivers\CMSIS\Device\ST\STM32L0xx\Include\system_stm32l0xx.h
?????文件??????10945??2015-12-15?15:15??DS18B20_USART\STM32L053\Drivers\CMSIS\Device\ST\STM32L0xx\Source\Templates\arm\startup_stm32l011xx.s
?????文件??????11221??2015-12-15?15:15??DS18B20_USART\STM32L053\Drivers\CMSIS\Device\ST\STM32L0xx\Source\Templates\arm\startup_stm32l021xx.s
?????文件??????10485??2015-12-15?15:15??DS18B20_USART\STM32L053\Drivers\CMSIS\Device\ST\STM32L0xx\Source\Templates\arm\startup_stm32l031xx.s
?????文件??????10736??2015-12-15?15:15??DS18B20_USART\STM32L053\Drivers\CMSIS\Device\ST\STM32L0xx\Source\Templates\arm\startup_stm32l041xx.s
?????文件??????11072??2015-12-15?15:15??DS18B20_USART\STM32L053\Drivers\CMSIS\Device\ST\STM32L0xx\Source\Templates\arm\startup_stm32l051xx.s
?????文件??????11259??2015-12-15?15:15??DS18B20_USART\STM32L053\Drivers\CMSIS\Device\ST\STM32L0xx\Source\Templates\arm\startup_stm32l052xx.s
?????文件??????11333??2015-12-15?15:15??DS18B20_USART\STM32L053\Drivers\CMSIS\Device\ST\STM32L0xx\Source\Templates\arm\startup_stm32l053xx.s
?????文件??????11084??2015-12-15?15:15??DS18B20_USART\STM32L053\Drivers\CMSIS\Device\ST\STM32L0xx\Source\Templates\arm\startup_stm32l061xx.s
?????文件??????11270??2015-12-15?15:15??DS18B20_USART\STM32L053\Drivers\CMSIS\Device\ST\STM32L0xx\Source\Templates\arm\startup_stm32l062xx.s
?????文件??????11328??2015-12-15?15:15??DS18B20_USART\STM32L053\Drivers\CMSIS\Device\ST\STM32L0xx\Source\Templates\arm\startup_stm32l063xx.s
?????文件??????11380??2015-12-15?15:15??DS18B20_USART\STM32L053\Drivers\CMSIS\Device\ST\STM32L0xx\Source\Templates\arm\startup_stm32l071xx.s
............此處省略556個(gè)文件信息
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