Dear:

In the PDF of IOT2040, it supports UARTs as 3 mode(232,485,422),

and  I can not find the selection from the hardware setting.

Besides, I find the libmraa support UART to read&write something, but I have not found any function to set the 3 modes(232,485,422).

So I want to know how to set the mode to working in the 485 mode, thanks a lot.

jianwen

Nobody have experience to use the RS485?

Up!  who could help me or give some information to prompt?

thanks so much!!!

Firstly thanks your answer to my question, and I have tested the sytem according your instruction.

It works well, but I also can not run my RS485 example to run normally.

1. based on my IOT2040 board, X30 as send terminal and X31as receive teriminal, I used RS232 as communication protocol:

     1) I used basic linux method as below:

         int fd0,fd1, sendBytes, receiveBytes; char sendBuffer[100], receiveBuffer[100];

          fd0 = open("/dev/ttyXR0",O_RDWR); fd1=open("/dev/ttyXR1",O_RDWR);

           strcpy(sendBuffer,"Hello monkeys!");

          sendBytes=write(fd0,sendBuffer,strlen(sendBuffer));

          receiveBytes = read(fd1,receiveBuffer,100);

        I run the code like this, but I can not get what I want to, the sendByte=94, and receiveBytes =109.

     I can not get the reason of that result, could you  tell me why?

  2) when I used the mraa library to do it as below: 

int dev0,dev1, sendBytes, receiveBytes; char sendBuffer[100], receiveBuffer[100];

dev0 = new mraa::Uart("/dev/ttyXR0"); dev1 = new mraa::Uart("/dev/ttyXR1");

strcpy(sendBuffer,"Hello monkeys!");

dev0->write(sendBuffer,strlen(sendBuffer));

receiveBytes = dev1->read(receiveBuffer,100);

I can get the receiveBytes=14, so the result is what I want to.

so why the mraa library could get the result but normally linux method can not?

2. based on my IOT2040 board, X30 as send terminal and X31as receive teriminal, I used RS485 as communication protocol:

In this situation I use the command that you help me know (swithserialmode) change the Uart mode as RS485.

however, when I used the mraa library to send data from XR30 I could see the data from oscilloscope, but the XR31 can not got any data from the bus, so I want to konow:

maybe there are some method to switch send or receive based on RS485?

because I use the IOT2000 system just some days, so please give me some supports, sincerely thanks for that!

thanks for you replay, I have 2 IOT2000 (2040):

hardware version:  2G110  and 2G111

same linux version: B01.01.00.00_01.08.00.01

 look forward your answer....

Best wishes

1. the Uart485.zip is my project which include the linux method and mraa method.

2. To my second question, I modify and test the two uart is same mode(RS485) and same buardrate.

thanks for your answer.

To bergmanu:

Your answer is very useful and help me to solve my problem.

I have tested it on my hardware, which is ok based on RS232 mode.

However, I can not receive the data based on RS485 mode, although I set the X30&X31 to RS485 mode and same buardrate. Could you help again? thank you