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1、樹莓派如何采集RS485數(shù)據(jù)1、RS485介紹RS485是有線傳輸串行數(shù)據(jù)的標，支持同時傳輸485總線上的多點數(shù)據(jù)。傳輸速率為10Mbps，傳輸距離可達50英尺。傳輸速率為100Kbps時，傳輸距離可達4000英尺。RS485總線通常為4芯或2芯，現(xiàn)在普遍采用2芯總線。一條總線最多支持32個設(shè)備。總線之間還可以串接，從而支持成百以上的節(jié)點。RS485主要技術(shù)規(guī)格如下：RS485specificationoverviewAttributeSpecificationCablingMulti-dropNumberofdevices32transmitt
2、ers32receiversCommunicationsmodeshalfduplexMaximumdistance4000feet@100kbpsMaximumdatarate10Mbps@50feetSignallingBalancedMark(data=1)condition1.5Vto5V(BgreaterthanA)Space(data=0)condition1.5Vto5V(AgreaterthanB>Driveroutputcurrentcapability250mA2、RS485和樹莓派的連接目前有一種RS485Shield的設(shè)備
3、，可以直接連接到樹莓派上。硬件連接圖如下：1、配置Updatesourcelist$sudoapt-getupdateInstallpython-pip$sudoapt-getinstallpython-pipUsepiptoinstallWiringPi(WiringPiisdesignedforraspberrypitobehavesimilarlytothatofthewiringlibraryunderArduino.?Afterthislibraryis?installed,c?orshellorpythoncanusethe?func
4、tiontoconfigureandcontrolGPIOsdirectly.?:$sudopipinstallwiringpiInstalledthe?associatedlibraryfilesofserialports:$sudoapt-getinstallpython-serial.TestwhethertheGPIOlibraryandtheseriallibraryisinstalledornot:$python$importRPi.GPIO$importserialIfthereisnoerror,thenthetwolibrari
5、esareinstalledcorrectly.Weneedtoconfigure?file‘/boot/cmdline.txt’toremovethekernelbootinginformationanddebugmessage:$sudonano/boot/cmdline.txtYoucanseethefollowinginformation:dwc_otg.lpm_enable=0console=ttyAMA0,115200kgdboc=ttyAMA0,115200console=tty1root=/dev/mmcblk0p2rootfst
6、ype=ext4elevator=deadlinerootwaitRemove“console=ttyAMA0,115200kgdboc=ttyAMA0,115200″sothattheinformationbecomes:dwc_otg.lpm_enable=0console=tty1root=/dev/mmcblk0p2rootfstype=ext4elevator=deadlinerootwaitDisableloginfromtheserialport:$sudonano/etc/inittabandcommentout”T0:23:re
7、spawn:/sbin/getty-LttyAMA0115200vt100″RestartRaspberryPi:$sudorebootNowyoucanuse/dev/ttyAMA0liketheregularCOMport.1、測試代碼Testcode(serial_test.py)?:12345678910111213importserial?port=”/dev/ttyAMA0″?usart=serial.Serial(port,9600)?usart.flushInput()?print(“serialtest:BaudRate=960
8、0″)?usart.write(“pleaseenterthecharacter:r”)?whileTrue:141516171819
