树莓派RS485调试指南.doc

树莓派RS485调试指南QQ 9230562891、 硬件准备2、 操作系统环境设置We need to modify two files: /boot/cmdline.txt and /etc/inittab. Modify /boot/cmdline.txt: Replace the original content: dwc_otg.lpm_enable=0 console=ttyAMA0,115200 kgdboc=ttyAMA0,115200 console=tty1 root=/dev/mmcblk0p2 rootfstype=ext4 elevator=deadline rootwait With: dwc_otg.lpm_enable=0 console=tty1 root=/dev/mmcblk0p2 rootfstype=ext4 elevator=deadline rootwait Modify /etc/inittab: Comment out the last line of /etc/inittab. To comment out, it simply addess a #. $ sudo vi /etc/inittab 1. T0:23:respawn:/sbin/getty -L ttyAMA0 115200 vt100 Save the changes, and reboot. We will get an UART with baud rate of 115200. 3、 驱动及相关软件设置Sudo apt-get install python-pipSudo apt-get install serial-python$ pythonimport RPi.GPIOimport serialIf there is no error , then the two libraries are installed correctly.退出：ctrl+d 或exit()如果在执行import时不报错，则认为这两个库已经正确安装。4、 RS485测试连线图如下：RS485-RS232的转换器有3个接口，A、B、接地。其中A口是TR+,B口是TR-。管脚定义如下：转换器的A口连RS485 shield的A口。转换器的B口连RS485 shield的B口。我们测试的方法是：PC机通过USB转232连232模块，232模块通过转换后接入到RS485 shield。PC机上启动超级终端，输入字符，在树莓派上能看到，就说明RS485 Shield能正确处理输入信号。启动超级终端，设置波特率为9600，控制流无、数据位8、停止位1、奇偶校验位无。在树莓派上运行python程序。源代码及运行方法如下：piraspberrypi:$ cat *.pyimport serialport=/dev/ttyAMA0usart=serial.Serial(port,9600)usart.flushInput()print(serial test Baudrae = 9600)usart.write(please enter the character:r)while True: if (usart.inWaiting()0): receive = usart.read() print ( receive:),receive usart.write(r) usart.write( send:) usart.write(r) usart.write(receive) usart.write(r)运行该