树莓派如何采集RS485数据

本文描述了树莓派采集RS485数据的方法和测试案例

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：

2、 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：

本文描述了树莓派采集RS485数据的方法和测试案例

本文描述了树莓派采集RS485数据的方法和测试案例

3、 配置

Update source list

$ sudo apt-get update

Install python-pip $ sudo apt-get install python-pip Use 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 the associated 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 serial

If there is no error , then the two libraries are installed correctly.

本文描述了树莓派采集RS485数据的方法和测试案例

We need to configure file /boot/cmdline.txt to remove the kernel booting information and debug message:

$ sudo nano / boot / cmdline.txt You 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 rootwait

Remove “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 / inittab

and comment out ” T0: 23: respawn :/ sbin / getty-L ttyAMA0 115200 vt100″

Restart Raspberry Pi:

$ sudo reboot

Now you can use / dev/ttyAMA0 like the regular COM port.

4、 测试代码

Test code(serial_test.py) : 1

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13 import serial port = ”/dev/ttyAMA0″ usart = serial.Serial(port,9600) usart.flushInput() print (“serial test: BaudRate = 9600″) usart.write(“please enter the character:\r”) while True:

本文描述了树莓派采集RS485数据的方法和测试案例

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if( usart.inWaiting()>0 ) : receive = usart.read(1) print ”receive: ”,receive usart.write(“ send: ’”) usart.write(receive) usart.write(“‘\r”)

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 9600

本文描述了树莓派采集RS485数据的方法和测试案例

After running serial_test.py, enter the characters in the X-CTU: