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Altera_Forum's avatar
Altera_Forum
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14 years ago

How to read RS232 ?

Hello all,

I have problem with UART, when i want to read serial data (hex byte message - something like bytes: 02,05,01,02,05 after this 10ms space and 03,05,xx,yy,zz etc.).

I have development kit DK-DSP-EP2S60 and when i connect the board, which send me bytes to the NIOS2 design with uart and in uClinux i use:

fd = open(S0_232, O_RDWR | O_NDELAY | O_NONBLOCK );

fd = open(S0_232, O_RDONLY | O_NOCTTY | O_NDELAY );

and when the program perform this command, the data from RxD RS232 are sended to the output TxD. I dont understand why ? (why it create loopback on RS232)

How is possible to read data from RS232 without loopback ? (how to set RS232 for reading only ?)

Thank you very much.

Jan Naceradsky, Czech Republic

7 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    I forgot:

    SO_232 is device "/dev/ttyS0"

    # define S0_232 "/dev/ttyS0"

    Jan Naceradsky
  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    Because the linux driver will be assuming you want tty semantics.

    You need to change the tty mode - see 'man termios' (at a guess).
  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    Thank you.

    I finally solved it with my collegue which advice me to add command

    stty -F /dev/ttyS3 sane -echo -icanon

    to rc file. This command stop the echo of input characters.

    And after open command in program i use:

    void init_rs232(void)

    {

    struct termios options;

    fd = open(S0_232, O_RDWR | O_NOCTTY | O_NDELAY );

    if (fd > 0)

    { fcntl(fd, F_SETFL, O_NONBLOCK);

    tcgetattr(fd, &options);

    options.c_cflag |= (CLOCAL | CREAD | CS8 );

    options.c_cc[VMIN] = 1;

    options.c_cc[VTIME] = 0;

    options.c_lflag = FLUSHO;

    tcsetattr(fd, TCSANOW, &options);

    printf("Init RS232 OK.\n");

    }

    }

    and now it works well.

    Jan Naceradsky
  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    The 'stty' comand probably does nothing useful - I'm not even sure the values persist once the device is closed.

    You are already disabling echo and icanon when you set c_lflag.
  • Altera_Forum's avatar
    Altera_Forum
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    13 years ago

    Yes, you are right, i cancel stty command in linux and use

    ---------------------------------------------------

    options.c_lflag &= ~(ICANON | ECHO | ISIG );

    in open function:

    fd = open(S0_232, O_RDWR | O_NOCTTY | O_NDELAY );

    // fd = open(S0_232, O_RDWR); // | O_NOCTTY | O_NDELAY );

    if (fd > 0)

    {

    fcntl(fd, F_SETFL, FNDELAY);

    tcgetattr(fd, &options);

    options.c_cflag |= (CLOCAL | CREAD );

    options.c_cflag &= ~PARENB; // set no parity, stop bits, data bits

    options.c_cflag &= ~CSTOPB;

    options.c_cflag &= ~CSIZE;

    options.c_cflag |= CS8;

    options.c_cc[VMIN] = 1;

    options.c_cc[VTIME] = 0;

    options.c_lflag &= ~(ICANON | ECHO | ISIG );

    tcsetattr(fd, TCSANOW, &options);

    }

    But when i read hex message (from PC to Altera NIOS2 system)

    16,11,01,00,00,00,00,80,00,7B

    the linux read

    16,01,00,00,00,00,80,00,7B

    and the second byte doesn't receive .... i read the termios on:

    http://slackware.osuosl.org/slackware-3.3/docs/mini/serial-port-programming

    and they say that 0x11 is DC1 which mean VSTART for XON and XOFF and i am not able to disable this software flow control.

    When i use setting

    options.c_cflag &= ~(IXON | IXOFF | IXANY); // no flow control

    or

    options.c_cflag &= ~CRTSCTS;

    it doesnt work. Read again:16,01,00,00,00,00,80,00,7B (and the 0x11 is missing).

    Do you have somebody program, which can read EVERY characters (hex - 00-FF) without any control meanings ?

    Is possible to disable control characters in options.c_cc[xxx] ?

    I retype

    options.c_cc[VSTART] = 0xFE;

    and the message is read ok, but echo was set ... why ?

    Where is error ?

    Jan, Czech Republic