树莓派如何采集RS485数据.docx

树莓派如何采集RS485数据1、 RS485介绍RS485是有线传输串行数据的标，支持同时传输485总线上的多点数据。传输速率为10Mbps，传输距离可达50英尺。传输速率为100Kbps时，传输距离可达4000英尺。RS485总线通常为4芯或2芯，现在普遍采用2芯总线。一条总线最多支持32个设备。总线之间还可以串接，从而支持成百以上的节点。RS485主要技术规格如下：RS485 specification overviewAttributeSpecificationCablingMulti-dropNumber of devices32 transmitters32 receiversCommunications modeshalf duplexMaximum distance4000 feet 100 kbpsMaximum data rate10 Mbps 50 feetSignallingBalancedMark (data = 1)condition1.5 V to 5 V (B greater than A)Space (data = 0)condition1.5 V to 5 V (A greater than BDriver output current capability250 mA2、 RS485和树莓派的连接目前有一种RS485 Shield的设备，可以直接连接到树莓派上。硬件连接图如下：3、 配置 Update source list$ sudo apt-get update Install python-pip$ sudo apt-get install python-pipUse pip to install WiringPi (WiringPi is designed for raspberry pi to behave similarly to that of the wiring library under Arduino. After this library is installed,c or shell or python can use the function to configure and control GPIOs directly. :$ sudo pip install wiringpi Installed theassociated library files of serial ports :$ sudo apt-get install python-serial.Test whether the GPIO library and the serial library is installed or not:$ python$ import RPi.GPIO$ import serialIf there is no error , then the two libraries are installed correctly. We need to configure file /boot/cmdline.txt to remove the kernel booting information and debug message:$ sudo nano / boot / cmdline.txtYou can see the following information:dwc_otg.lpm_enable = 0 console = ttyAMA0, 115200 kgdboc = ttyAMA0, 115200 console = tty1 root = / dev/mmcblk0p2 rootfstype = ext4 elevator = deadline rootwaitRemove “console = ttyAMA0, 115200 kgdboc = ttyAMA0, 115200 so that the information becomes:dwc_otg.lpm_enable = 0 console = tty1 root = / dev/mmcblk0p2 rootfstype = ext4 elevator = deadline rootwait Disable log in from the serial port:$ sudo nano / etc / inittaband comment out ” T0: 23: respawn :/ sbin / getty-L ttyAMA0 115200 vt100 Restart Raspberry Pi:$ sudo rebootNow you can use / dev/ttyAMA0 like the regular COM port.4、 测试代码Test code(serial_test.py):12345678910111213141516171819202122232425import serialport = ”/dev/ttyAMA0usart = serial.Serial(port,9600)usart.flushInput()print (“serial test: BaudRate = 9600)usart.write(“please enter the character:r”)while True:if( usart.inWaiting()0 ) :receive = usart.read(1)print ”receive: ”,receiveusart.write(“ send: ”)usart.write(receive)usart.write(“r”)5、 1 x RaspberryPi6、 1 x RS485shieldfor Raspberry Pi7、8、 3 x Male to male jumper wires9、 1 x RS232-RS485 converter10、 1 x 9DB male of serial-to-USB cable:11、12、 Wiring:13、 RS485 Shield A- RS232-RS485 converter T/R + 14、 RS485 Shield B- RS232-RS485 converter T/R- 15、 RS485 Shield GND - RS232-RS485 converter GND 16、17、6、基于RS232转RS485的测试例程硬件连接方式：硬件管脚对应关系：RS485 Shield A- RS232-RS485 converter T/R + RS485 Shield B- RS232-RS485 converter T/R- RS485 Shield GND - RS232-RS485 converter GND After the wiring is done, launch a serial terminal. We use X-CTU in our case, and set the baud rate to 9600After running serial_test.py, enter the characters in the X-CTU:18、 After the wiring is don